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{{Short description|Ruler of the Roman Empire}}
{{About||the ruler of the archaic Roman Kingdom|King of Rome|the dual chief magistrate during the Republic|Roman consul|a chronological list|List of Roman emperors}}
{{Infobox monarchy
| border            = imperial
| royal_title       = Emperor
| realm             = the Roman Empire
| coatofarms        = Better Imperial Aquila.png
| coatofarmscaption = Imperial {{lang|la|[[Aquila (Roman)|aquila]]}}
| image             = Glyptothek München – 18.04.2022 – Augustus Bevilacqua (5).jpg
| caption           = Bust of [[Augustus]] wearing the {{lang|la|[[corona civica]]}}
| first_monarch     = [[Augustus]]
| last_monarch      = {{Ubl|[[Theodosius I]] ([[Roman Empire|unified]])|[[Romulus Augustulus]] ([[Western Roman Empire|Western]]){{Efn|Although [[Romulus Augustulus]] ({{Reign|475|476}}) is often regarded as the last Western emperor, his predecessor [[Julius Nepos]] continued to be recognized in the Eastern court as the legitimate ruler of the West.{{Sfn|Bury|2012|p=408}}}}|[[Constantine XI Palaiologos|Constantine XI]] ([[Byzantine Empire|Eastern]])}}
| style             = [[Imperator]], [[Caesar (title)|Caesar]], [[Augustus (honorific)|Augustus]], [[Princeps]], Dominus Noster, [[Autokrator]] or [[Basileus]] (depending on period)
| appointer         = [[Senate of the Roman Empire|Senate]] (official), [[Military of ancient Rome|Roman military]]
| began             = 16 January 27 BC
| ended             = {{Ubl|9 May 480 (Western)|29 May 1453 (Eastern)}}
}}

The '''Roman emperor''' was the ruler and monarchical [[head of state]] of the [[Roman Empire]], starting with the granting of the title {{lang|la|[[Augustus (title)|augustus]]}} to [[Octavian]] in 27&nbsp;BC.{{Sfn|Watkin|2017|p=37}} The term ''[[emperor]]'' is a modern convention, and did not exist as such during the Empire. When a given Roman is described as becoming ''emperor'' in English, it generally reflects his accession as {{lang|la|augustus}}, and later as {{tlit|grc|[[basileus]]}}. Another title used was {{lang|la|[[imperator]]}}, originally a military honorific, and {{lang|la|[[Caesar (title)|caesar]]}}, originally a [[cognomen]]. Early emperors also used the title {{lang|la|[[princeps]]}} ("first one") alongside other [[Roman Republic|Republican]] titles, notably {{lang|la|[[Roman consul|consul]]}} and {{lang|la|[[pontifex maximus]]}}.

The legitimacy of an emperor's rule depended on his control of the [[Roman army]] and recognition by the [[Roman Senate|Senate]]; an emperor would normally be proclaimed by his troops, or by the Senate, or both. The first emperors reigned alone; later emperors would sometimes rule with co-emperors to secure the succession or to divide the administration of the empire between them. The office of emperor was thought to be distinct from that of a {{lang|la|[[Rex (title)|rex]]}} ("king"). Augustus, the first emperor, resolutely refused recognition as a monarch.{{Sfn|Galinsky|2005|pp=13-14}} For the first three hundred years of Roman emperors, efforts were made to portray the emperors as leaders of the Republic, fearing any association with the kings who ruled Rome prior to the Republic.

From [[Diocletian]], whose reformed [[tetrarchy]] divided the position into one emperor in the [[Western Roman Empire|West]] and one in the [[Byzantine Empire|East]], emperors ruled in an openly monarchic style.{{Sfn|Williams|1997|p=147}} Although succession was generally hereditary, it was only hereditary if there was a suitable candidate acceptable to the army and the bureaucracy,{{Sfn|Heather|2005|p=28}} so the principle of automatic inheritance was not adopted, which often led to several [[Roman usurper|claimants to the throne]]. Despite this, elements of the republican institutional framework (Senate, consuls, and magistrates) were preserved even after the end of the Western Empire.

[[Constantine the Great]], the first Christian emperor, moved the capital from Rome to [[Constantinople]], formerly known as [[Byzantium]], in 330 AD. Roman emperors had always held high religious offices; under Constantine there arose the specifically Christian idea that the emperor was God's chosen ruler on earth, a special protector and leader of the Christian Church, a position later termed [[Caesaropapism]]. In practice, an emperor's authority on Church matters was frequently subject to challenge. The [[Western Roman Empire]] collapsed in the late 5th century after multiple invasions by [[Germanic peoples|Germanic]] barbarian tribes, with no recognised claimant to Emperor of the West remaining after the death of [[Julius Nepos]] in 480. Instead, the Eastern emperor [[Zeno (emperor)|Zeno]] proclaimed himself as the sole emperor of a theoretically undivided Roman Empire (although in practice he had no authority in the West). The subsequent Eastern emperors ruling from Constantinople styled themselves as "{{tlit|grc|Basileus}} of the Romans" ({{langx|grc|βασιλεύς Ῥωμαίων}}, {{tlit|grc|Basileus Romaíon}}) but are often referred to in modern scholarship as [[Byzantine emperors]].

The [[papacy]] and [[Germanic kingdoms]] of the West acknowledged the Eastern emperors until the accession of [[Empress Irene]] in 797. After this, the papacy created a rival lineage of Roman emperors in western Europe, the [[Holy Roman Emperor]]s, which ruled the [[Holy Roman Empire]] for most of the period between 800 and 1806. These emperors were never recognized in Constantinople and their coronations resulted in the medieval [[problem of two emperors]]. The last Eastern emperor was [[Constantine XI Palaiologos]], who died during the [[Fall of Constantinople]] to the [[Ottoman Empire]] in 1453. After conquering the city, [[List of sultans of the Ottoman Empire|Ottoman sultans]] adopted the title "{{lang|la|Caesar}} of the Romans" ({{lang|ota|[[kayser-i Rûm]]}}). A Byzantine group of claimant emperors existed in the [[Empire of Trebizond]] until its conquest by the Ottomans in 1461, although they had used a modified title since 1282.

== Background and beginning ==
{{See also|Crisis of the Roman Republic}}
[[File:Augustus depicted as a Magistrate, Ny Carlsberg Glyptotek, Copenhagen (14747345348).jpg|thumb|[[Augustus]] depicted as a [[Roman magistrate|magistrate]] at the [[Ny Carlsberg Glyptotek]]]]

Modern historians regard [[Augustus]] as the first emperor, whereas [[Julius Caesar]] is considered the last [[Roman dictator|dictator]] of the [[Roman Republic]], a view that is shared by the Roman writers [[Plutarch]], [[Tacitus]], and [[Cassius Dio]].{{Sfn|Barnes|2009|pp=278-279}} Conversely, the majority of Roman writers, including [[Pliny the Younger]], [[Suetonius]] and [[Appian]], as well as most of the ordinary people of the Empire, thought of Julius Caesar as the first emperor.{{Sfn|Barnes|2009|pp=279-282}} Caesar did indeed rule the Roman state as an [[Autocracy|autocrat]], but he failed to create a stable system to maintain himself in power.<ref>{{Harvnb|Sandys|1921|p=285. "To describe him as the founder of the Empire is an error, for he bequeathed to Augustus rather warnings than examples"}}; {{Cite book |last=Craven |first=Maxwell |title=The Imperial Families of Ancient Rome |date=2019 |publisher=Fonthill Media |pages=[https://books.google.com/books?id=VEbCDwAAQBAJ&pg=PT29 27]}}</ref> His rise to power was the result of a long and gradual decline in which the Republic fell under the influence of powerful generals such as [[Gaius Marius]] and [[Sulla]].{{Sfn|Watkin|2017|pp=33–37}}

At the end of the Republic no new or singular title indicated the individual who held supreme power. Insofar as ''emperor'' could be seen as the English translation of the Latin {{Lang|la|[[imperator]]}}, then Julius Caesar had been an emperor, like several Roman generals before him. Instead, by the end of the [[Caesar's civil wars]], it became clear that there was certainly no consensus to return to [[King of Rome|the old-style monarchy]], but that the period when several officials would fight one another had come to an end.

Julius Caesar, and then Augustus after him, accumulated offices and titles of the highest importance in the Republic, making the power attached to those offices permanent, and preventing anyone with similar aspirations from accumulating or maintaining power for themselves. [[Julius Caesar]] had been ''[[pontifex maximus]]'' since 64 BC; held the offices of [[Roman consul|consul]] and [[Roman dictator|dictator]] five times since 59 BC, and was appointed [[Dictator perpetuo|dictator in perpetuity]] in 44 BC, shortly before [[Assassination of Julius Caesar|his assassination]]. He had also become the ''de facto'' sole ruler of Rome in 48 BC, when he defeated his last opposition at the [[Battle of Pharsalus]]. His killers proclaimed themselves as the ''[[liberatores]]'' ("liberators") and the restorers of the Republic, but their rule was cut short by Caesar's supporters, who almost immediately established a new dictatorship.

[[File:Kameo Augustus mit Tritonengespann KHM IXa 56.jpg|thumb|left|[[Cameo (carving)|Cameo]] of Augustus in a {{Lang|la|[[quadriga]]}} drawn by [[Triton (mythology)|tritons]] at the [[Kunsthistorisches Museum]], Vienna]]

In his will, Caesar appointed his grandnephew [[Octavian]] as his heir and adopted son. He inherited his property and lineage, the loyalty of most of his allies, and – again through a formal process of senatorial consent – an increasing number of the titles and offices that had accrued to Caesar. In August 43 BC, following the [[War of Mutina|death of both consuls of the year]], Octavian marched to Rome and forced the Senate to elect him consul. He then formed the [[Second Triumvirate]] alongside [[Mark Antony]] and [[Lepidus]], dividing the Roman world among them. Lepidus was sidelined in 36 BC, and relations between Octavian and Antony soon deteriorated. In September 31 BC, Octavian's [[Battle of Actium|victory at Actium]] put an end to any effective opposition and confirmed his supremacy over Rome.

In January 27 BC, Octavian and the Senate concluded the so-called "[[Constitutional reforms of Augustus|First settlement]]". Until then Octavian had been ruling the state with his powers as ''triumvir'', even though the Triumvirate itself disappeared years earlier. He announced that he would return the power to the [[Senate and People of Rome]], but this was only an act. The Senate confirmed Octavian as ''[[princeps]]'', the "[[first among equals]]", and gave him control over almost all Roman provinces for a tenure of ten years. This limitation was only superficial, as he could renew his powers indefinitely. In addition, the Senate awarded him the appellation of ''[[Augustus (title)|augustus]]'' ("elevated"). The honorific itself held no legal meaning, but it denoted that Octavian (henceforth [[Augustus]]) now approached divinity, and its adoption by his successors made it the ''de facto'' main title of the emperor. He also received the [[Civic Crown|civic crown]] alongside several other insignias in his honor. Augustus now held supreme and indisputable power, and even though he still received subsequent grants of powers, such as the granting of ''[[tribunicia potestas]]'' in 23 BC, these were only ratifications of the powers he already possessed.<ref>{{Harvnb|Bowman|Champlin|Lintott|1996|pp=76-87}}; {{Harvnb|Eck|Takács|2007|pp=50-58}}.</ref>

Most modern historians use 27 BC as the start date of the Roman Empire. This is mostly a symbolic date, as the Republic had essentially disappeared many years earlier. Ancient writers often ignore the legal implications of Augustus' reforms and simply write that he "ruled" Rome following the murder of Caesar, or that he "ruled alone" after the death of Mark Antony.<ref>[[Eutropius (historian)|Eutropius]], [https://www.livius.org/sources/content/eutropius-short-history/eutropius-short-history-7/ ''Breviarium'' 7.8] "From that period he held the government as sole ruler for forty-four years, for during the twelve previous years he had held it in conjunction with Antony and Lepidus. Thus from the beginning of his reign to the end were fifty-six years."</ref><ref>[[Jerome]], ''[[Chronicon (Jerome)|Chronichon]]'', [https://www.tertullian.org/fathers/jerome_chronicle_03_part2.htm 184th Olympiad]. "2nd [ruler] of the Romans, Octavianus Caesar Augustus reigned for 56 years and 6 months; from whom the kings [[basileus]] of the Romans are called ''Augusti''."</ref> Most Romans thus simply saw the "emperor" as the individual that ruled the state, with no specific title or office attached to him.

Augustus actively prepared his adopted son [[Tiberius]] to be his successor and pleaded his case to the Senate for inheritance on merit. After Augustus' death in AD 14, the Senate confirmed Tiberius as {{Lang|la|princeps}} and proclaimed him as the new ''augustus''. Tiberius had already received ''imperium maius'' and ''tribunicia potestas'' in AD 4, becoming legally equal to Augustus but still subordinate to him in practice.{{Sfn|Bowman|Champlin|Lintott|1996|p=201}} The "imperial office" was thus not truly defined until the accession of [[Caligula]], when all of Tiberius' powers were automatically transferred to him as a single, abstract position that was symbolized by his sacred title of ''augustus''.<ref>{{Harvnb|Bowman|Champlin|Lintott|1996|p=119}}; {{Harvnb|Eck|Takács|2007|pp=50-58}}; {{Cite journal |last=Rich |first=John |date=2012 |title=Making the emergency permanent: auctoritas, potestas and the evolution of the principate of Augustus |url=https://www.academia.edu/3323294 |journal=Des réformes augustéennes |pages=80–82}}</ref>

== Powers under the Principate ==
{{Politics of ancient Rome}}

The legal authority of the emperor derived from an extraordinary concentration of individual powers and offices that were extant in the Republic and developed under Augustus and later rulers, rather than from a new political office. Under the Republic, these powers would have been split between several people, who would each exercise them with the assistance of a colleague and for a specific period of time. Augustus held them all at once by himself, and with no time limits; even those that nominally had time limits were automatically renewed whenever they lapsed.<ref>[https://www.britannica.com/place/ancient-Rome/Augustan-art-and-literature#ref26662 Ancient Rome] at [[Encyclopedia Britannica]]</ref> The Republican offices endured and emperors were regularly elected to the most prominent of them: the [[Roman consul|consulship]] and [[Roman censor|censorship]].<ref>{{Cite encyclopedia |date=1875 |title=A Dictionary of Greek and Roman Antiquities |publisher=[[University of Chicago]] |url=https://penelope.uchicago.edu/Thayer/E/Roman/Texts/secondary/SMIGRA*/Censor.html |last=Murray |first=John |pages=260–266}}</ref> This early period of the Empire is known as the "[[Principate]]", derived from the title ''princeps'' used by the early emperors.

The most important bases of the emperor's power were his supreme power of command (''[[imperium|imperium maius]]'') and tribunician power (''[[tribunicia potestas]]'') as personal qualities, separate from his public office.<ref>{{Harvnb|Bowman|Champlin|Lintott|1996|pp=117-118}}; {{Harvnb|Petit|2022|pp=46-47}}; {{Harvnb|Sandys|1921|pp=287-288}}.</ref> Originally, the powers of command where divided in consular ''imperium'' for Rome and proconsular ''imperium'' for the [[Roman province|provinces]]. This division became obsolete in 19 BC when Augustus was given consular ''imperium'' – despite leaving the consulship in 23 BC – and thus control over all troops. This overwhelming power was referred to as ''imperium maius'' to indicate its superiority to other holders of ''imperium'', such as the [[proconsul]]s of the few senatorial provinces and allies such as [[Marcus Vipsanius Agrippa|Agrippa]].<ref>{{Cite book |last=Atkins |first=Jed W. |title=Roman Political Thought |date=2018 |publisher=Cambridge University Press |isbn=978-1-1071-0700-7 |pages=[https://books.google.com/books?id=LkFPDwAAQBAJ&pg=PA30 29]-30}}; {{Harvnb|Mousourakis|2017|pp=238-239}}; {{Harvnb|Petit|2022|pp=46-47}}.</ref> The governors appointed to the imperial provinces only answered to the emperor himself, who could maintain or replace them at will.{{Sfn|Mousourakis|2017|pp=238-239}}

[[File:Silver Denarius of Augustus (CNG).jpg|thumb|205x205px|left|[[Denarius]] of [[Augustus]] (18 BC).{{Efn|The legend reads: {{Smallcaps|'''[[SPQR|spqr]]''' imp(erator) caesari aug(ustus) co(n)s(ul) xi tri(bunicia) pot(estas) vi}}; meaning "consul for the 11th time, [wielder of the] tribunician power for the 6th time".}}]]

The tribunician power (''tribunicia potestas''), first assumed by Augustus in 23 BC, gave him authority over the [[tribune of the plebs]] without having to actually hold the office – a tribune was by definition a [[plebeian]], whereas Augustus, although born into a plebeian family, had become a [[Patrician (ancient Rome)|patrician]] when he was adopted into the [[Julia (gens)|''gens Julia'']].{{Sfn|Mousourakis|2017|pp=238-239}} By adopting the role of a tribune, Augustus was presenting himself as the representative of the common man and the protector of democracy.<ref>{{Harvnb|Mousourakis|2014|p=18}}; {{Harvnb|Sandys|1921|pp=287-288}}.</ref> As always, this was not a sudden grant of power; Augustus had been receiving several powers related to the tribunes, such as [[sacrosanctity]], since 36&nbsp;BC.<ref>{{Harvnb|Petit|2022|pp=46-47}}; {{Harvnb|Sandys|1921|pp=287-288}}</ref> With this powers, he could [[veto]] any act or proposal of any magistrate, propose laws and convoke the Senate.<ref>{{Harvnb|Mousourakis|2014|p=18}}; {{Harvnb|Mousourakis|2017|pp=238–239}}.</ref> His sacrosanctity also made him untouchable, and any offence against him could be treated as a crime of treason.<ref>{{Harvnb|Mousourakis|2014|p=18}}; {{Harvnb|Sandys|1921|pp=287-288}}.</ref> The tribunician power was arguably the most stable and important of the emperor's powers.<ref>{{Harvnb|Sandys|1921|p=231}}; {{Harvnb|Petit|2022|p=145}}; {{Harvnb|Mousourakis|2017|p=242}}.</ref> Despite being a perpetual title, it was always renewed each year, which often coincided with the beginning of a new regnal year (although "[[regnal year]]s" were not officially adopted until [[Justinian I]]).<ref>{{Harvnb|Sandys|1921|p=231}}; {{Cite book |last1=Bagnall |first1=Roger Shaler |title=Chronological Systems of Byzantine Egypt |last2=Worp |first2=Klaas Anthony |author-link2=Klaas Worp |date=2004 |publisher=Brill |isbn=978-9-0041-3654-0 |pages=[https://books.google.com/books?id=CUT6UnqXVzQC&pg=PA4 4]}}</ref>{{Efn|For a further discussion of the ''tribunicia potestas'' and the role of the Senate, see: {{Cite book |last=Rowe |first=Greg |title=Princes and Political Cultures: The New Tiberian Senatorial Decrees |date=2002 |publisher=University of Michigan Press |isbn=978-0-4721-1230-2 |pages=[https://books.google.com/books?id=XkcTaWGAgAAC&pg=PA41 41]-66}}}}

The office of [[Roman censor|censor]] was not fully absorbed into the imperial office until the reign of [[Domitian]], who declared himself "perpetual censor" (''censor perpetuus'') in AD 85. Before this, the title had been only used by [[Claudius]] (47), [[Vespasian]] and [[Titus]] (both in 73).<ref>{{Harvnb|Sandys|1921|p=231}}; {{Harvnb|Petit|2022|p=145}}.</ref>

The emperor also had power over religious affairs, which led to the creation of a [[Roman imperial cult|worship cult]]. Augustus became ''[[pontifex maximus]]'' (the chief priest of the [[College of Pontiffs]]) in 12 BC, after the death of the former ''triumvir'' [[Marcus Aemilius Lepidus (triumvir)|Lepidus]].<ref>{{Harvnb|Petit|2022|pp=46-47}}; {{Harvnb|Mousourakis|2017|pp=238-239}}.</ref> Emperors from the reign of [[Gratian]] ({{R.|375|383}}) onward used the style ''[[pontifex inclytus]]'' ("honorable pontiff"). The title of ''pontifex maximus'' was eventually adopted by the [[Pope|bishops of Rome]] during the [[Renaissance]].<ref>{{Citation |last=Curran |first=John R. |title=From Petrus to Pontifex Maximus |date=2020 |work=The Early Reception and Appropriation of the Apostle Peter (60–800 CE) |pages=43–57 |url=https://brill.com/display/book/edcoll/9789004425682/BP000015.xml |publisher=Brill |isbn=978-9-0044-2568-2}}</ref> The last known emperors to use the title were [[Valentinian III]] and [[Marcian]], in the 5th century.{{Sfn|Hekster|2022|p=36}}

The only surviving document to directly refer to the emperor's power is the ''[[Lex de imperio Vespasiani]]'', written shortly after [[Vespasian]]'s formal accession in December 69. The text, of which only the second part survives, states that Vespasian is allowed to: make treaties; hold sessions and propose motions to the Senate; hold extraordinary sessions with legislative power; endorse candidates in elections; expand the ''[[pomerium]]''; and use [[discretionary power]] whenever necessary. The text further states that he is "not bound by laws", and that any previous act was [[Ex post facto law|retroactively]] considered legitimate.<ref name="KaiusTuori">{{Citation |last=Tuori |first=Kaius |title=lex de imperio Vespasiani |date=2019 |work=[[Oxford Classical Dictionary]] |url=https://oxfordre.com/classics/display/10.1093/acrefore/9780199381135.001.0001/acrefore-9780199381135-e-8283 |isbn=978-0-1993-8113-5}}</ref> There is no mention of ''imperium'' nor ''tribunicia potestas'', although these powers were probably given in the earlier clauses.{{Sfn|Sandys|1921|p=280}} There is also no mention of any "imperial office", and the title of "emperor" is never used. The imperial titles are treated as inseparable of the person, which is reflected in the name ''Imperator Caesar [[Vespasian]]us Augustus''. This ''Lex'' sometimes related to the ''[[Lex regia (imperial)|Lex regia]]'' ("royal law") mentioned in the {{Lang|la|[[Corpus Juris Civilis]]}} of Eastern emperor [[Justinian I]] ({{R.|527|565}}), who cites the early 3rd-century writer [[Ulpian]]. This was probably a later construct, as its very name, which derives from ''[[Rex (title)|rex]]'' ("king"), would have been utterly rejected in the West.<ref>{{Cite book |last=Canning |first=Joseph |url=https://books.google.com/books?id=RR_KAgAAQBAJ&pg=PA8 |title=A History of Medieval Political Thought: 300–1450 |date=2014 |publisher=Routledge |isbn=978-1-1366-2342-4}}</ref> The Eastern Greek-speaking half of the Empire had always regarded the emperors as open monarchs (''[[Basileus|basileis]]''), and called them as such.{{Sfn|Bury|2012|pp=15-16}}<ref name="Wif">{{Cite book |last=Wifstrand |first=Albert |title=Epochs and Styles: Selected Writings on the New Testament, Greek Language and Greek Culture in the Post-classical Era |date=2005 |publisher=Mohr Siebeck |isbn=978-3-1614-8627-2 |pages=[https://books.google.com/books?id=GTwfoIkLN2MC&pg=PA159 158]-163}}</ref>

== Succession and legitimacy ==
The weakest point of the Augustan institution was its lack of a clear succession system.<ref>{{Harvnb|Petit|2022|pp=52-54}}; {{Harvnb|Mousourakis|2014|p=20}}.</ref> Formally announcing a successor would have revealed Augustus as a monarch, so he and subsequent emperors opted to adopt their best candidates as their sons and heirs. [[Primogeniture]] was not relevant in the early Empire, although emperors still attempted to maintain a familiar connection between them; [[Tiberius]], for example, married [[Julia the Elder]], making him [[Augustus]]' son-in-law.

[[Vespasian]], who took power after the collapse of the [[Julio-Claudian dynasty]] and the tumultuous [[Year of the Four Emperors]], was the first emperor to openly declare his sons, [[Titus]] and [[Domitian]], as his sole heirs, giving them the title of ''[[Caesar (title)|caesar]]''.<ref>{{Harvnb|Petit|2022|pp=52-54}}; {{Harvnb|Tellegen-Couperus|2002|p=76}}; {{Harvnb|Kelly|Hug|2022|pp=60-62}}</ref> The [[Roman Senate|Senate]] still exercised some power during this period, as evidenced by his decision to declare [[Nero]] a "public enemy",<ref>{{Cite book |last=Overmeire |first=Sam Van |title=Studies in latin Literature and Roman History |date=2012 |editor-last=Deroux |editor-first=Carl |volume=XVI |pages=472–491 |chapter=Nero, the Senate and People of Rome: Reactions to an Emperor's Image |chapter-url=https://www.academia.edu/1893505}}</ref> and did influence in the succession of emperors. Following the murder of Domitian in AD 96, the Senate declared [[Nerva]], one of their own, as the new emperor.{{Sfn|Tellegen-Couperus|2002|p=76}} His "dynasty", the [[Nerva–Antonine dynasty|Antonine]], continued the adoptive system until the reign of [[Marcus Aurelius]] ({{R.|161|180}}). Marcus was the first emperor to rule alongside other emperors, first with his adoptive brother [[Lucius Verus]], who succeeded jointly with him, and later with his son [[Commodus]], who was proclaimed co-''[[Augustus (title)|augustus]]'' in 177.<ref>{{Harvnb|Tellegen-Couperus|2002|p=76}}; {{Harvnb|Kelly|Hug|2022|pp=60-62}}</ref>{{Efn|There was, however, much precedent. The [[Roman consul|consulate]] of the [[Roman Republic|Republic]] was a twin magistracy, and earlier emperors had often had a subordinate lieutenant with many imperial offices. Many emperors had planned a joint succession in the past – [[Augustus]] planned to leave [[Gaius Caesar|Gaius]] and [[Lucius Caesar]] as joint emperors on his death; Tiberius wished to have [[Caligula]] and [[Tiberius Gemellus]] do so as well; as [[Claudius]] with [[Nero]] and [[Britannicus]]. All of these arrangements had ended in failure, either through premature death (Gaius and Lucius) or murder (Gemellus and Britannicus).<ref>{{Cite book |last=Birley |first=Anthony |title=Marcus Aurelius |date=2000 |publisher=[[Routledge]] |pages=117, 153 n. 157}}</ref>}}

Despite being the son of a previous emperor and having nominally shared government with him, Commodus' rule ended with his murder at the hands of his own soldiers. From his death in 192 until the 5th century, there was scarcely a single decade without succession conflicts and civil war. During this period, very few emperors died of natural causes.<ref name="NathanSmolin">{{Cite thesis |last=Smolin |first=Nathan I. |title=Christ the Emperor: Roman Emperor and Christian Theology in the 4th Century AD |date=2021 |degree=Doctoral |publisher=University of North Carolina |url=https://cdr.lib.unc.edu/concern/dissertations/gq67k073z?locale=en |doi=10.17615/wg7y-3h07 |pages=22–23}}</ref> Such problems persisted in the later Eastern Empire, where emperors had to often appoint co-emperors to secure the throne. Despite often working as a hereditary monarchy, there was no law or single principle of succession.<ref>{{Cite book |last1=Kazhdan |first1=Aleksandr Petrovich |title=People and Power in Byzantium: An Introduction to Modern Byzantine Studies |last2=Constable |first2=Giles |date=1982 |publisher=Dumbarton Oaks |isbn=978-0-8840-2103-2 |page=[https://books.google.com/books?id=bs2uV8eBVIcC&pg=PA146 146]}}</ref>

[[File:Dedicatory inscription Ostia Antica 2006-09-08.jpg|thumb|282x282px|[[Latin]] inscription dedicated to [[Septimius Severus]] and [[Caracalla]] in [[Ostia Antica]], AD 196.{{Efn|The text reads: {{Small|IMP CAES DIVI MARCI ANTONINI PII FILIVS / DIVI COMMODI FRATER DIVI ANTONINI PII / NEPOS DIVI HADRIANI PRONEP DIVI TRAIANI / PARTHICI ABNEPOS DIVI NERVAE ADNEPOS / L SEPTIMIVS SEVERVS PIVS PERTINAX AVG / ARABICVS ADIABENICVS PP PONTIF MAX / TRIBVNIC POTEST IIII IMP VIII COS II ET / MARCVS AVRELIVS ANTONINVS CAESAR / DEDICAVERVNT}}. "Dedicated to Imperator Caesar, son of the divine [[Marcus Aurelius|Marcus Antoninus Pius]], brother of the divine [[Commodus]], grandson of the divine [[Antoninus Pius]], great-grandson of the divine [[Hadrian]], great-great grandson of the divine [[Trajan]] [[Parthicus|conqueror of Parthia]], great-great-great-grandson of the divine [[Nerva]], [[Lucius Septimius Severus|Lucius Septimius Severus Pius Pertinax Augustus]], conqueror of Arabia and Adiabene, [[father of the fatherland]], [[pontifex maximus|supreme priest]], having the [[tribunician power]] for the fourth time, [[imperator]] for the eighth time, [[consul]] for the second time, and [[Caracalla|Marcus Aurelius Antoninus Caesar]]."}}]]
Individuals who claimed imperial power "illegally" are referred to as "[[Roman usurper|usurpers]]" in modern scholarship. Ancient historians refer to these rival emperors as "[[tyrant]]s". In reality, there was no distinction between emperors and usurpers, as many emperors started as rebels and were retroactively recognized as legitimate. The ''[[Lex de imperio Vespasiani]]'' explicitly states that all of Vespasian's actions are considered legal even if they happened before his recognition by the Senate.<ref name="KaiusTuori"/> Ultimately, "legitimacy was a ''post factum'' phenomenon."{{Sfn|McEvoy|2013|pp=36–41}} [[Theodor Mommsen]] famously argued that "here has probably never been a regime in which the notion of legitimacy is as absent as that of the Augustan principate".{{Sfn|Omissi|2018|pp=33–34}} Imperial propaganda was often used to legitimize or de-legitimize certain emperors. The ''[[Chronicon Paschale]]'', for example, describes [[Licinius]] as having been killed like "those who had briefly been usurpers before him".<ref name="cp"/> In reality, Licinius was the legitimate emperor of the West (having been appointed by [[Galerius]]), while Constantine was the real "usurper" (having been proclaimed by his troops).<ref>{{Cite journal |last=Humphries |first=Mark |date=2008 |title=From Usurper to Emperor: The Politics of Legitimation in the Age of Constantine |url=https://www.academia.edu/477631 |journal=[[Journal of Late Antiquity]] |volume=1 |pages=82–100 |doi=10.1353/jla.0.0009 |s2cid=154368576}}</ref>

There were no true objective legal criteria for being acclaimed emperor beyond acceptance by the [[Roman army]], which was really the true basis of imperial power. Common methods used by emperors to assert claims of legitimacy, such as support of the army, blood connections (sometimes fictitious) to past emperors, distributing one's own coins or statues, and claims to pre-eminent virtue through propaganda, were pursued just as well by many usurpers as they were by legitimate emperors.<ref name="NathanSmolin"/> [[Septimius Severus]] notably declared himself as the adoptive son of the long-deceased [[Marcus Aurelius]], hence why he named [[Caracalla]] after him.<ref>{{Cite book |last=Rantala |first=Jussi |title=The Ludi Saeculares of Septimius Severus: The Ideologies of a New Roman Empire |date=2017 |publisher=Taylor & Francis |isbn=978-1-3519-7039-6 |page=[https://books.google.com/books?id=ikYlDwAAQBAJ&pg=PA95 95]}}</ref> Later Eastern imperial dynasties, such as the [[Doukai]] and [[Palaiologoi]], claimed descent from [[Constantine the Great]].<ref>{{Cite encyclopedia |title=Doukas family |encyclopedia=Encyclopaedia of the Hellenic World, Asia Minor |publisher=Foundation of the Hellenic World |location=Athens |url=http://www.ehw.gr/l.aspx?id=7855 |access-date=17 April 2012 |last=Krsmanović |first=Bojana |date=11 September 2003}}; {{Cite encyclopedia |date=2008 |title=Palaeologan Dynasty (1259–1453) |encyclopedia=Encyclopaedia of the Hellenic World |publisher=Foundation of the Hellenic World |location=Asia Minor |url=http://asiaminor.ehw.gr/Forms/fLemmaBody.aspx?lemmaid=11799 |access-date=2020-06-17 |ref=CITEREFEncyclopaedia of the Hellenic World}}</ref>

What turns a "usurper" into a "legitimate" emperor is typically that they managed to gain the recognition of a more senior, legitimate, emperor, or that they managed to defeat a more senior, legitimate emperor and seize power.<ref name="LiesbethClaes">{{Cite journal |last=Claes |first=Liesbeth |date=2015 |title=Coins with power?: imperial and local messages on the coinage of the usurpers of the second half of the third century |url=https://scholarlypublications.universiteitleiden.nl/access/item%3A2865541/view |journal=Jaarboek voor Munt- en Penningkunde |volume=102 |pages=15–60 |oclc=948592865}}</ref>{{Sfn|Omissi|2018|pp=17ff}} Modern historiography has not yet defined clear legitimacy criteria for emperors, resulting in some emperors being included or excluded from different lists. The year 193 has traditionally been called the "[[Year of the Five Emperors]]", but modern scholarship now identifies [[Clodius Albinus]] and [[Pescennius Niger]] as usurpers because they were not recognized by the [[Roman Senate]].<ref>{{Cite book |last=Bennett |first=Julian |title=Trajan: Optimus Princeps |date=2003 |publisher=Routledge |isbn=978-1-1347-0914-4 |page=[https://books.google.com/books?id=FdSEAgAAQBAJ&pg=PA49 49]}}</ref> Recognition by the Senate is often used to determine the legitimacy of an emperor,<ref name="LiesbethClaes"/> but this criterion is not always followed. [[Maxentius]] is sometimes called an usurper because he did not have the recognition of [[Tetrarchy|Tetrarchs]],<ref name="MichaelKulikowski">{{Cite book |last=Kulikowski |first=Michael |url=https://books.google.com/books?id=QXM9SH4EALgC |title=Rome's Gothic Wars: From the Third Century to Alaric |date=2006 |publisher=Cambridge University Press |isbn=978-1-1394-5809-2 |page=199}}</ref><ref>{{Cite web |title=Collections Online {{!}} British Museum |url=https://www.britishmuseum.org/collection/term/BIOG140709 |access-date=2023-08-09 |website=britishmuseum.org}}</ref> but he held Rome for several years, and thus had the recognition of the Senate.{{Sfn|Omissi|2018|p=131}} Other "usurpers" controlled, if briefly, the city of Rome, such as [[Nepotianus]] and [[Priscus Attalus]]. In the East, the possession of [[Constantinople]] was the essential element of legitimacy,<ref>{{The Latin Renovatio of Byzantium|chapter=The Imperial Ideology|pp=61–101}}</ref> yet some figures such as [[Procopius]] are treated as usurpers. Rival emperors who later gained recognition are not always considered legitimate either; [[Vetranio]] had the formal recognition by [[Constantius II]] yet he is still often regarded as a usurper,{{Sfn|Omissi|2018|pp=185–186}}<ref name="HughElton">{{Cite book |last=Elton |first=Hugh |title=The Roman Empire in Late Antiquity: A Political and Military History |date=2018 |publisher=Cambridge University Press |isbn=978-0-5218-9931-4 |page=[https://books.google.com/books?id=oOlwDwAAQBAJ&pg=PA112 112]}}</ref> similarly to [[Magnus Maximus]], who was briefly recognized by [[Theodosius I]].<ref name="HughElton"/> Western emperors such as [[Magnentius]], [[Eugenius]] and [[Magnus Maximus]] are sometimes called usurpers,<ref name="MichaelKulikowski"/> but [[Romulus Augustulus]] is traditionally regarded as the last Western emperor, despite never receiving the recognition of the Eastern emperor [[Zeno (emperor)|Zeno]].

== Later developments ==

[[File:Statua di Costantino ai musei capitolini.jpg|thumb|The [[Colossus of Constantine]]. Portraits after the [[Tetrarchy]] stopped including realistic features, as the emperor began to be seen as a symbol rather than an individual.<ref>{{Cite book |last1=Ruiz |first1=María Pilar García |title=Emperors and Emperorship in Late Antiquity: Images and Narratives |last2=Puertas |first2=Alberto J. Quiroga |date=2021 |publisher=Brill |isbn=978-9-0044-4692-2 |pages=[https://books.google.com/books?id=xo8cEAAAQBAJ&pg=PA141 141]–146}}</ref>]]
The period after the [[Principate]] is known as the [[Dominate]], derived from the title ''dominus'' ("lord") adopted by [[Diocletian]]. During his rule, the emperor became an absolute ruler and the regime became even more monarchical.{{Sfn|Aguilera-Barchet| 2014|p=54}} The emperors adopted the [[diadem]] crown as their supreme symbol of power, abandoning the subtleties of the early Empire.{{Sfn|Bury|2012|p=10}}

Beginning in the late 2nd century, the Empire began to suffer a series of political and economic crises, partially because it had overexpanded so much.{{Sfn|Aguilera-Barchet|2014|p=54}} The ''[[Pax Romana]]'' ("Roman peace") is often said to have ended with the tyrannical reign of Commodus. His murder was followed by the accession of [[Septimius Severus]], the victor of the [[Year of the Five Emperors]]. It was during his reign that the role of the army grew even more, and the emperors' power increasingly depended on it.<ref>{{Harvnb|Tellegen-Couperus|2002|p=77}}; {{Harvnb|Digeser|2000|pp=20–24}}.</ref><ref name="PatSouthern">{{Cite book |last=Southern |first=Pat |author-link=Pat Southern |title=The Roman Empire from Severus to Constantine |date=2003 |publisher=Routledge |isbn=978-1-1345-5381-5 |page=[https://books.google.com/books?id=-ySCAgAAQBAJ&pg=PA254 254]}}</ref> The murder of his last relative, [[Severus Alexander]], led to the [[Crisis of the Third Century]] (235–285), a 50-year period that almost saw the end of the Roman Empire.{{Sfn|Mousourakis|2014|p=20}} The last vestiges of Republicanism were lost in the ensuing anarchy. In 238, the Senate attempted to regain power by proclaiming [[Pupienus]] and [[Balbinus]] as their own emperors (the first time since [[Nerva]]).<ref>{{Harvnb|Hekster|2022|p=189}}; {{Harvnb|Digeser|2000|p=25}}.</ref> They managed to usurp power from [[Maximinus Thrax]], but they were killed within two months. With the rise of the "soldier emperors", the city and Senate of Rome began to lose importance. Maximinus and [[Carus]], for example, did not even set foot on the city.<ref name="PatSouthern"/> Carus' successors [[Carinus]] and [[Numerian]], the last of the Crisis emperors, did not bother to assume the ''tribunicia potestas'' either.{{Sfn|Tellegen-Couperus|2002|p=77}}

After reuniting the Roman Empire in 285, [[Diocletian]] began a series of reforms to restore stability. Reaching back to the oldest traditions of job-sharing in the Republic, Diocletian established at the top of this new structure the [[Tetrarchy]] ("rule of four") in an attempt to provide for smoother succession and greater continuity of government. Under the Tetrarchy, Diocletian set in place a system of two emperors (''augusti'') and two subordinates that also served as heirs (''caesares''). When an emperor retired (as Diocletian and [[Maximian]] did in 305) or died, his ''caesar'' would succeed him and in turn appoint a new ''caesar''.{{Sfn|Watkin|2017|p=53}} Each pair ruled over a half of the Empire, which led to the creation of a [[Western Roman Empire|Western]] and [[Eastern Roman Empire]], a division that eventually became permanent.{{Sfn|Digeser|2000|p=26}} This division had already a precedent in the joint rule of [[Valerian (emperor)|Valerian]]/[[Gallienus]] and [[Carus]]/[[Carinus]].{{Sfn|Digeser|2000|p=25}}

Diocletian justified his rule not by military power, but by claiming [[Divine right of kings|divine right]].{{Sfn|Digeser|2000|p=26}} He imitated Oriental divine kingship and encouraged the reverence of the emperor, making anything related to him ''sacer'' (sacred).<ref>{{Harvnb|Watkin|2017|p=56}}; {{Harvnb|Bury|2012|p=12}}.</ref> He declared himself ''Jovius'', the son of [[Jupiter (mythology)|Jupiter]], and his partner Maximian was declared ''Herculius'', son of [[Hercules]].{{Sfn|Digeser|2000|pp=27–30}} This divine claim was maintained after the rise of Christianity, as emperors regarded themselves as the chosen rulers of God.{{Sfn|Aguilera-Barchet|2014|p=54}}

The emperor no longer needed the Senate to ratify his powers, so he became the sole source of law. These new laws were no longer shared publicly and were often given directly to the [[praetorian prefect]]s – originally the emperor's bodyguard, but now the head of the new [[praetorian prefecture]]s – or with private officials.{{Sfn|Watkin|2017|p=56}} The emperor's personal court and administration traveled alongside him, which further made the Senate's role redundant. Consuls continued to be appointed each year, but by this point, it was an office often occupied by the emperor himself,{{Efn|Consuls still maintained some privileges during the later Empire, but at times it was only an honorary office. Some emperors gave the title to their children. For instance; [[Valentinian II]] assumed the consulate of 376 at the age of 5 and [[Honorius (emperor)|Honorius]] did the same in 386 at the age of 2.}} who now had complete control over the bureaucratic apparatus.{{Sfn|Aguilera-Barchet|2014|p=55}} Diocletian did preserve some Republican traditions, such as the ''tribunicia potestas''.{{Sfn|Sandys|1921|p=231}} The last known emperor to have used it was [[Anastasius I Dicorus|Anastasius I]], at the start of the 6th century. Anastasius was also the last attested emperor to use the traditional titles of ''[[proconsul]]'' and ''[[pater patriae]]''.{{Sfn|Hekster|2022|p=42}} The last attested emperor to use the title of consul was [[Constans II]], who was also the last Eastern emperor to visit Rome.<ref>Cameron, A., & Schauer, D. (1982). [https://www.jstor.org/stable/299119 The Last Consul: Basilius and His Diptych]. ''The Journal of Roman Studies'' '''72''': 126–145.</ref> It's possible that later emperors also used it as an honorary title, as the office of consul was not [[Basilika|abolished]] until 892, during the reign of [[Leo VI the Wise|Leo VI]].<ref>{{Cite book |last=Riedel |first=Meredith |title=Leo VI and the Transformation of Byzantine Christian Identity |publisher=Cambridge University Press |date=2018 |isbn=978-1-1070-5307-6 |pages=[https://books.google.com/books?id=4jJlDwAAQBAJ&pg=PA100 100]}}</ref>

During the Dominate it became increasingly common for emperors to raise their children directly to ''augustus'' (emperor) instead of ''caesar'' (heir), probably because of the failure of the Tetrarchy. This practice had first been applied by [[Septimius Severus]], who proclaimed his 10-year-old son [[Caracalla]] as ''augustus''. He was followed by [[Macrinus]], who did the same with his 9-year-old son [[Diadumenian]], and several other emperors during the Crisis. This became even more common from the 4th century onwards. [[Gratian]] was proclaimed emperor at the age of 8, and his co-ruler and successor [[Valentinian II]] was proclaimed emperor at the age of 4.{{Sfn|McEvoy|2013|pp=1–8}} Many child emperors such as [[Philip II (Roman emperor)|Philip II]] or [[Diadumenian]] never succeeded their fathers. These co-emperors all had the same honors as their senior counterpart, but they did not share the actual government, hence why junior co-emperors are usually not counted as real emperors by modern or ancient historians. There was no title to denote the "junior" emperor; writers used the vague terms of "second" or "little emperor".{{Sfn|Bury|2012|pp=5–6}}{{Efn|A [[:File:The concession of privileges mosaic.jpg|mosaic in Italy]] shows [[Constantine IV]] ({{R.|668|686}}) alongside his co-emperors [[Heraclius (son of Constans II)|Heralius]] and [[Tiberius (son of Constans II)|Tiberius]]. Constantine is called ''maior imperator'', Heraclius and Tiberius being only ''imperator''.}}

Despite having a successful reign himself, Diocletian's tetrarchic system [[Civil wars of the Tetrarchy|collapsed]] as soon as he retired in 305. [[Constantine the Great|Constantine I]], the son of tetrarch [[Constantius Chlorus|Constantius I]], reunited the empire in 324 and imposed the principle of hereditary succession which Diocletian intended to avoid.<ref>{{Cite book |last=Kim |first=Young Richard |title=The Cambridge Companion to the Council of Nicaea |date=2021 |publisher=Cambridge University Press |isbn=978-1-1084-2774-6 |pages=[https://books.google.com/books?id=TioNEAAAQBAJ&pg=PA29 27]–29}}</ref> Constantine was also the first emperor to convert to [[Christianity]], and emperors after him, especially after its officialization under [[Theodosius I]], saw themselves as the protectors of the Church.{{Sfn|Watkin|2017|p=62}} The territorial divisions of the Tetrarchy were maintained, and for most of the following century the Empire was ruled by two senior emperors, one in the West (with [[Milan]] and later [[Ravenna]] as capital) and another in the East (with [[Constantinople]] as capital).{{Efn|Starting with [[Diocletian]], almost every other emperor ruled alongside an equal or junior co-emperor. The only two emperors of this period to rule over the entire Roman Empire for their entire reign were [[Julian (emperor)|Julian II]] and [[Jovian (emperor)|Jovian]], both of which only ruled about a year. [[Valentinian I]], who succeeded Jovian, immediately divided the empire between himself and his brother [[Valens]]. After this the empire was again reunited by [[Theodosius I]], but he died only a few months later.}}

This division became permanent on the death of [[Theodosius I]] in 395, when he was succeeded by his sons [[Honorius (emperor)|Honorius]] and [[Arcadius]].{{Sfn|Watkin|2017|p=61}} The two halves of the Empire, while later functioning as ''de facto'' separate entities, were always considered and seen, legally and politically, as separate administrative divisions of a single, insoluble state by the Romans of the time.<ref>{{Cite journal |last=Sandberg |first=Kaj |date=2008 |title=The So-Called Division of the Roman Empire in AD 395: Notes on a Persistent Theme in Modern Historiography |url=https://journal.fi/arctos/article/view/85853 |journal=Arctos |volume=42 |pages=199–213 |issn=0570-734-X}}{{Harvnb|Bury|2012|p=408}}.</ref>

{{Multiple image
| align       = left
| total_width = 380
| image1      = RomulusAugustus.jpg
| image2      = Julius Nepos Tremissis.jpg
| footer      = [[Roman coins]] (''[[Solidus (coin)|tremissis]]'') of [[Romulus Augustulus]] and [[Julius Nepos]], the last emperors of the [[Western Roman Empire]].
}}

In the [[Western Roman Empire|West]], the office of emperor soon degenerated into being little more than a puppet of Germanic [[Magister militum|generals]] such as [[Aetius (magister militum)|Aetius]] and [[Ricimer]]; the last emperors of the West being known as the "shadow emperor".<ref>{{Cite journal |last=McEvoy |first=Meaghan |date=2017 |title=Shadow emperors and the choice of Rome (455–476 AD) |url=https://www.academia.edu/36522939 |journal=Antiquité Tardive |volume=25 |pages=95–112 |doi=10.1484/J.AT.5.114852 |issn=1250-7334}}</ref> In 476, the [[Heruli]] [[Odoacer]] overthrew the child-emperor [[Romulus Augustulus]], made himself [[king of Italy]] and shipped the imperial regalia to the [[Emperor Zeno]] in Constantinople. Historians mark this date as the date of the [[fall of the Western Roman Empire]], although by this time there was no longer any "Empire" left, as its territory had reduced to Italy. [[Julius Nepos]], who was overthrown and expelled to [[Dalmatia]] in favor of Romulus, continued to claim the title until his murder in 480. The Eastern court recognized this claim and Odoacer minted coins in his name, although he never managed to exercise real power.<ref>{{Cite book |last=Demo |first=Željko |title=Studia Numismatica Labacensia Alexandro Jeločnik Oblata |publisher=Narodni muzej |date=1988 |editor-last=Kos |editor-first=Peter |location=Ljubljana |chapter=The Mint in Salona: Nepos and Ovida (474–481/2) |editor-last2=Demo |editor-first2=Željko |chapter-url=https://www.academia.edu/519543}}</ref> The death of Nepos left [[Zeno (emperor)|Zeno]] as the sole emperor of a (technically) reunited Roman Empire.{{Sfn|Bury|2012|p=408}}

=== Byzantine period ===
The Roman Empire survived in the East for another 1000 years, but the marginalization of the former heartland of Italy to the empire had a profound cultural impact on the empire and its emperor, which adopted a more [[Hellenistic]] character.{{Efn|The Eastern Empire is often referred as the "[[Byzantine Empire]]" (from [[Byzantium]], the original name of [[Constantinople]]) in modern scholarship, although it was still technically the same state of Antiquity.<ref>There is much discussion on the term "Byzantine", as well as when does exactly the "Dominate" end and the "Byzantine" period begins. {{Cite book |last=Mango |first=Cyril |author-link=Cyril Mango |url=https://books.google.com/books?id=ZZ82psJ2pLEC |title=The Oxford History of Byzantium |publisher=OUP Oxford |date=2002 |isbn=0-1981-4098-3 |pages=1–5}}</ref> Their Greek-speaking inhabitants were called ''[[Romaioi]]'' (Ῥωμαῖοι), and were still considered Romans by themselves and the populations of Eastern Europe and the Near East, although they always had a more Greek-oriented culture because of the conquests of [[Alexander the Great]]. The [[Ottoman Turks]] still used the term "[[Rûm]]" (Rome) when referring to the Eastern Empire.<ref>{{Cite book |last=El-Cheikh |first=Nadia Maria |title=Byzantium Viewed by the Arabs |date=2004 |publisher=Harvard University Press |isbn=978-0-9328-8530-2 |pages=[https://books.google.com/books?id=QC03pKNpfaoC&pg=PA22 22ff]}}</ref> After the fall of Empire, the [[Tsardom of Russia]] proclaimed [[Moscow]] as the "[[Third Rome]]", regarding Constantinople as the "Second Rome".<ref>{{Cite book |title=The Blackwell Dictionary of Eastern Christianity |publisher=Blackwell Publishing |date=1999 |isbn=978-0-6312-3203-2 |editor-last=Parry |editor-first=Ken |location=Malden, MA |page=490 |editor-last2=Melling |editor-first2=David}}</ref> The evolution of the church in the no-longer imperial city of Rome and the church in Constantinople also began to follow divergent paths, culminating in the [[schism of 1054]] between the [[Roman Catholic]] and [[Eastern Orthodox]] faiths.}}

The Eastern emperors continued to be recognized in the [[Barbarian kingdoms|Western kingdoms]] until the accession of [[Irene of Athens|Irene]] ({{R.|797|802}}), the first [[Queen regnant|empress regnant]]. The Italian heartland was recovered during the reign of [[Justinian I]] ({{R.|527|565}}), but this was reverted by the end of the century. Rome technically remained [[Exarchate of Ravenna|under imperial control]], but was completely surrounded by the [[Lombards]]. Africa was [[Early Muslim conquests|lost to the Arabs]] in the early 7th century, and Rome eventually fell to the Lombards in 751, during the reign of [[Constantine V]]. The Frankish king [[Pepin the Short]] defeated them and received the favour of [[Pope Stephen II]], who became the head of the [[Papal States]]. Pepin's son, [[Charlemagne]], was crowned ''[[Holy Roman Emperor|Imperator Romanorum]]'' (the first time ''Imperator'' was used as an actual regnal title) by [[Pope Leo III]] in Christmas AD 800, thus ending the recognition of the Eastern emperor.{{Sfn|Kazhdan|1991|p=413}} Western rulers also began referring to the Empire as the "Greek Empire", regarding themselves as the true successors of Rome.<ref>{{Cite book |last1=Fouracre |first1=Paul |title=Late Merovingian France: History and Hagiography, 640–720 |last2=Gerberding |first2=Richard A. |date=1996 |publisher=Manchester University Press |isbn=978-0-7190-4791-6 |page=[https://books.google.com/books?id=uifpAAAAIAAJ&pg=PA345 345]}}</ref>

[[File:Manuel II Helena sons.JPG|thumb|Miniature depicting [[Manuel II Palaiologos]] and his family, 1404.{{Efn|Manuel is referred as {{Small|ΒΑCΙΛΕΥC ΚΑΙ ΑΥΤΟΚΡΑΤΩΡ ΡΩΜΑΙΩΝ Ο ΠΑΛΑΙΟΛΟΓΟC ΚΑΙ ΑΕΙ ΑΥΓΟΥCΤΟC}} ("[[basileus]] and [[autokrator]] of the Romans, Palaiologos, always [[augusta (title)|augoustos]]"). His wife [[Helena Dragaš]] is referred as {{Small|ΑΥΓΟΥCΤΑ ΚΑΙ ΑΥΤΟΚΡΑΤΟΡΙCΑ ΡΩΜΑΙΩΝ Η ΠΑΛΑΙΟΛΟΓΙΝΑ}} ("[[augusta (title)|augusta]] and [[autokrator]]a of the Romans, wise Palaiologina"); his son [[John VIII Palaiologos|John VIII]] is called ''basileus'', while [[Andronikos Palaiologos (son of Manuel II)|Andronikos]] and [[Theodore II Palaiologos|Theodore]] are called ''[[despotes]]''.<ref>{{Cite book |last=Hilsdale |first=Cecily J. |title=Byzantine Art and Diplomacy in an Age of Decline |date=2014 |publisher=Cambridge University Press |isbn=978-1-1070-3330-6 |pages=[https://books.google.com/books?id=ghaTAgAAQBAJ&pg=PA26 260]–262}}</ref>}}]]
The inhabitants of the Eastern half of the Empire always saw the emperor as an open monarch. Starting with [[Heraclius]] in 629, Roman emperors styled themselves "[[basileus]]", the traditional title for Greek monarchs used since the times of [[Alexander the Great]].<ref>{{Cite book |last=Kaegi |first=Walter E. |title=Heraclius, Emperor of Byzantium |date=2003 |publisher=[[Cambridge University Press]] |isbn=978-0-5218-1459-1 |page=[https://books.google.com/books?id=tlNlFZ_7UhoC&pg=PA194 194]}}; {{Harvnb|Kazhdan|1991|p=264}}.</ref> The title was used since the early days of the Empire and became the common imperial title by the 3rd century, but did not appear in official documents until the 7th century.<ref>{{Harvnb|Bury|2012|pp=15–16}}; {{Harvnb|Kazhdan|1991|p=264}}.</ref> [[Michael I Rangabe]] ({{R.|811|813}}) was the first emperor to actually use the title of "Roman emperor" (βασιλεύς Ῥωμαίων, ''Basileus Romaíon''). This was a response to the new line of emperors created by Charlemagne{{Snd}}although he was recognized as ''basileus'' of the [[Franks]].{{Sfn|Kazhdan|1991|p=264}} By the 9th century the full imperial title became "''basileus'' and ''[[autokrator]]'' of the Romans", usually translated as "Emperor and Autocrat of the Romans".{{Sfn|Kazhdan|1991|p=235}}{{Efn|A variation of the title was later adopted by the [[Emperor of Russia|Russian emperors]], who styled themselves as "Emperor and Autocrat of All the Russias".<ref>{{Cite web |title=Chapter Six On the Title of His Imperial Majesty and the State Coat of Arms |url=http://imperialhouse.ru/en/dynastyhistory/dinzak1/446.html |url-status=live |archive-url=https://web.archive.org/web/20231022120345/https://imperialhouse.ru/en/dynastyhistory/dinzak1/446.html |archive-date=Oct 22, 2023 |website=The Fundamental State Laws of the Russian Empire |publisher=Russian Imperial House}}</ref> In Russian, the title employs the title ''[[imperator]]'' (император) instead of the traditional ''[[tsar]]'' (царь), which had the same meaning.}} The title ''autokrator'' was also used to distinguish a junior co-emperor (''basileus'') from his senior colleague (''basileus autokrator'').{{Sfn|Kazhdan|1991|p=235}} By the times of the [[Palaiologos]], there were two distinct ceremonies for the accession of an emperor: first an acclamation as ''basileus'', and later a [[Coronation of the Byzantine emperor|coronation]] as ''autokrator'' (which also included being raised on a shield). These rites could happen years apart.<ref name="RuthMacrides">{{Cite book |last1=Macrides |first1=Ruth |title=Pseudo-Kodinos and the Constantinopolitan Court: Offices and Ceremonies |last2=Munitiz |first2=J. A. |last3=Angelov |first3=Dimiter |date=2016 |publisher=Routledge |isbn=978-1-3170-7395-6 |pages=https://books.google.com/books?id=I9UYDQAAQBAJ&pg=PT302 302]–305}}</ref>

The Eastern Empire became not only an [[absolute monarchy]] but also a [[theocracy]]. According to [[George Ostrogorsky]], "the absolute power of the Roman emperor was further increased with the advent of Christian ideas".<ref name="GeorgeOstrogorsky">{{Cite journal |last=Ostrogorsky |first=George |date=1956 |title=The Byzantine Emperor and the Hierarchical World Order |journal=The Slavonic and East European Review |volume=35 |issue=84 |pages=1–14 |issn=0037-6795 |jstor=4204790}}</ref> This became more evident after the [[Early Muslim conquests|Muslim conquests]] of the 7th century, which gave Byzantine imperialism a new sense of purpose.<ref>{{Cite book |last=Magdalino |first=Paul |url=https://ia903404.us.archive.org/11/items/Book_1274/The%20Cambridge%20Intellectual%20History%20of%20Byzantium.pdf |title=The Cambridge Intellectual History of Byzantium |date=2017 |publisher=Cambridge University Press |isbn=978-1-1070-4181-3 |editor-last=Kaldellis |editor-first=Anthony |pages=575–598 |chapter=Basileia: The Idea of Monarchy in Byzantium, 600–1200 |editor-last2=Siniossoglou |editor-first2=Niketas |chapter-url=https://www.cambridge.org/core/books/cambridge-intellectual-history-of-byzantium/basileia-the-idea-of-monarchy-in-byzantium-6001200/F9A9F7ABAC5870A29B6701189427753A}}</ref> The emperor was the subject of a series of rites and ceremonies, including a [[Coronation of the Byzantine emperor|formal coronation]] performed by the [[Patriarch of Constantinople]].<ref name="GeorgeOstrogorsky"/> The Byzantine state is often said to have followed a "[[Caesaropapism|Caesaropapist]]" model, where the emperor played the role of ruler and head of the Church, but there was often a clear distinction between political and secular power.<ref>{{Cite web |title=Caesaropapism {{!}} Byzantine Empire, Autocracy & Ecclesiastical Power |url=https://www.britannica.com/topic/caesaropapism |website=[[Encyclopædia Britannica]]}}</ref>

The line of Eastern emperors continued uninterrupted until the [[sack of Constantinople]] and the establishment of the [[Latin Empire]] in 1204. This led to the creation of three lines of emperors in exile: the [[Empire of Nicaea|emperors of Nicaea]], the [[List of Trapezuntine emperors|emperors of Trebizond]], and the short-lived [[Empire of Thessalonica|emperors of Thessalonica]]. The Nicean rulers have been traditionally regarded as the "legitimate" emperors of this period, as they recovered Constantinople and restored the Empire in 1261.{{Efn|This is reflected in the [[regnal number|numbering]] used by scholars: [[John V Palaiologos]] is numbered after [[John III Vatatzes]] and [[John IV Laskaris]], both emperors of Nicaea, but the other rival emperors are treated as entirely new lines of succession.}} The [[Empire of Trebizond]] continued to exist for another 200 years, but from 1282 onwards its rulers used the modified title of "Emperor and Autocrat of all the East, [[Kingdom of Iberia|the Iberians]], and the [[Perateia]]", accepting the Niceans as the sole Roman emperors.{{Sfn|Kazhdan|1991|p=1047}} However, the Byzantine Empire had been reduced mostly to Constantinople, and the rise of other powers such as [[Serbian Empire|Serbia]] and [[Second Bulgarian Empire|Bulgaria]] forced the Byzantines to recognize their rulers as ''basileus''. Despite this, emperors continued to view themselves as the rulers of an "universal empire".<ref name="GeorgeOstrogorsky"/> During the last decades of the Empire, power was once again shared between multiple emperors and colleagues, each ruling from their own capital, notably during the long reign of [[John V Palaiologos|John V]].<ref name="ElizabethJeffreys">{{Cite book |last1=Jeffreys |first1=Elizabeth |title=The Oxford Handbook of Byzantine Studies |last2=Haldon |first2=John F. |last3=Cormack |first3=Robin |date=2008 |publisher=Oxford University Press |isbn=978-0-1992-5246-6 |pages=[https://books.google.com/books?id=liFKua_cWL8C&pg=PA293 291]–293}}</ref> Constantinople finally [[Fall of Constantinople|fell to the Ottoman Turks]] in 1453; its last emperor, [[Constantine XI Palaiologos]], died in battle. The last vestiges of the empire, [[Despotate of the Morea|Morea]] and [[Fall of Trebizond|Trebizond]], fell in 1461.<ref name="ElizabethJeffreys"/>

==Titles==
=== ''Imperator'' ===
{{Main|Imperator}}

{{Multiple image
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| caption1    = [[Denarius]] of Julius Caesar marked {{Smallcaps|caesar imp(erator)}}
| image2      = INC-2056-a Ауреус. Веспасиан. Ок. 75—79 гг. (аверс).png
| caption2    = [[Aureus]] of [[Vespasian]] marked<br/>{{Smallcaps|imp(erator) caesar vespasianus aug(ustus)}}
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}}
The title ''imperator'' – from ''imperare'', "to command" – dates back to the [[Roman Republic]] and was given to victorious commanders by their soldiers. They held ''[[imperium]]'', that is, military authority. The Senate could then award the extraordinary honor of a [[Roman triumph|triumph]]; the commander then retained the title until the end of his [[Roman magistrate|magistracy]]. In Roman tradition, the first triumph was that of [[Romulus]], the founder of Rome, but the first attested use of ''imperator'' was in 189 BC, on the triumph of [[Lucius Aemilius Paullus Macedonicus|Aemilius Paulus]]. It was a title held with great pride: [[Pompey]] was hailed ''imperator'' more than once, as was [[Sulla]] and [[Julius Caesar]].<ref name="SimonHornblower">{{Cite book |last1=Hornblower |first1=Simon |title=The Oxford Classical Dictionary |last2=Spawforth |first2=Antony |last3=Eidinow |first3=Esther |date=2012 |isbn=978-0-1995-4556-8 |pages=[https://books.google.com/books?id=bVWcAQAAQBAJ&pg=PA728 728]–729 |chapter=Imperator |doi=10.1093/acrefore/9780199381135.013.3268 |chapter-url=https://doi.org/10.1093/acrefore/9780199381135.013.3268}}</ref> However, as noted by [[Cassius Dio]], the meaning of the title changed under the new monarchy, and came to denote "the possession of the supreme power".<ref name="RussellFoster">For a discussion of ''imperium'' and ''imperator'', see {{Cite book |last=Foster |first=Russell |title=Mapping European Empire: Tabulae imperii Europaei |date=2015 |publisher=Routledge |isbn=978-1-3175-9307-2 |pages=11–52 |chapter=All roads lead to Rome |chapter-url=https://books.google.com/books?id=D8kBCgAAQBAJ&pg=PA35}}</ref> Both Dio and [[Suetonius]] refer to Caesar as the first one to assume ''imperator'' as a proper name (a ''praenomen imperatoris''), but this seems to be an [[anachronism]].{{Sfn|Syme|1958}} The last ordinary general to be awarded the title was [[Junius Blaesus]] in AD 22, after which it became a title reserved solely for the sovereign.<ref name="SimonHornblower"/>

Augustus used ''Imperator'' instead of his first name (''[[praenomen]]''), becoming ''Imperator Caesar'' instead of ''Caesar Imperator''.<ref name="SimonHornblower"/> From this the title slowly became a synonym of the office, hence the word "emperor". [[Tiberius]], [[Caligula]] and [[Claudius]] avoided using the title, but it is recorded that Caligula was hailed ''imperator'' by the Senate on his accession, indicating that it was already considered an integral part of the dignity.<ref>{{Cite book |last=Barrett |first=Anthony A. |title=Caligula: The Corruption of Power |date=2002 |publisher=Routledge |isbn=978-1-1346-0988-8 |page=[https://books.google.com/books?id=G0WFAgAAQBAJ&pg=PA53 53]}}</ref> It was not until the late reign of [[Nero]], in AD 66, that ''imperator'' became once more part of the emperor's nomenclature.<ref>{{Cite book |last=Sutherland |first=C.H.V. |title=Roman Imperial Coinage |date=2018 |publisher=Spink Books |isbn=978-1-9126-6736-9 |volume=1 |page=[https://books.google.com/books?id=WnTKDwAAQBAJ&pg=PA133 133]}}</ref> Virtually all emperors after him used the ''praenomen imperatoris'', with only a few variations under his successors [[Galba]] and [[Vitellius]].{{Sfn|Hammond|1957}} The original meaning of the title continued to be used for a time, with emperors registering the number of times they were hailed ''imperator''.<ref name="RussellFoster"/> The title became the main appellation of the ruler by the time of [[Vespasian]].<ref name="SimonHornblower"/><ref name="Paterculus81"/>

After the [[Tetrarchy]], emperors began to be addressed as ''dominus noster'' ("our Lord"), although ''imperator'' continued to be used. The appellation of ''dominus'' was known and rejected by Augustus, but ordinary men of the Empire used it regularly. It began to used in official context starting with [[Septimius Severus]], and was first officially adopted in coinage by [[Aurelian]].{{Sfn|Greenidge|1901|pp=352–355}}

In the East, ''imperator'' was translated as ''[[autokrator]]'' ("self-ruler"), a title that continued to be used until the end of the Empire. This is the modern Greek word for "emperor" ([[wiktionary:αυτοκράτορας| αυτοκράτορας]]). There are still some instances of ''imperator'' in official documents as late as the 9th century. Its last known use was on 866–867 coins of [[Michael III]] and his co-emperor [[Basil I]], who are addressed as ''imperator'' and ''rex'' respectively.<ref>{{Cite book |last=Grierson |first=Philip |url=https://archive.org/details/docoins-3 |title=Catalogue of Byzantine Coins, vol. 3: Leo III to Nicephorus III, 717–1081 |publisher=Dumbarton Oaks |date=1973 |isbn=0-8840-2012-6 |location=Washington D.C. |pages=456–467}}</ref> In the West, ''imperator'' was transformed into a monarchical title by [[Charlemagne]], becoming the official Latin title of the [[Holy Roman Empire]].

===''Caesar''===
{{Main|Caesar (title)}}
Originally the ''[[cognomen]]'' (third name) of the dictator [[Julius Caesar|Gaius Julius Caesar]], which was then inherited by Augustus and his relatives. Augustus used it as a family name (''[[Nomen gentilicium|nomen]]''), styling himself as ''Imp. Caesar'' instead of ''Imp. Julius Caesar''.{{Sfn|Syme|1958}} However, the nomen was still inherited by women (such as [[Julia the Younger]]) and appear in some inscriptions.<ref>[[Corpus Inscriptionum Latinarum|CIL]] [https://db.edcs.eu/epigr/epi_einzel.php?s_sprache=de&p_belegstelle=CIL+02%2C+01660&r_sortierung=Belegstelle 2, 1660]; [https://db.edcs.eu/epigr/epi_einzel.php?s_sprache=de&p_belegstelle=CIL+06%2C+00930&r_sortierung=Belegstelle 6, 930]. Tiberius is sometimes called ''Tiberius Julius Caesar'' instead of the more common ''Tiberius Caesar''.</ref> After the death of [[Caligula]], Augustus' great-grandson, his uncle [[Claudius]] was proclaimed emperor. He was not an official member of the [[Julia gens]],{{Sfn|Loewenstein|1973|p=349}} but he was the grandson of [[Octavia the Younger|Octavia]], Augustus' sister, and thus still part of the family.<ref>{{Cite book |last=Pagán |first=Victoria Emma |title=Tacitus |date=2017 |publisher=Bloomsbury Publishing |isbn=978-1-7867-3132-6 |pages=[https://books.google.com/books?id=t-mKDwAAQBAJ&pg=PA29 28]–30}}</ref>

Following the suicide of Nero, the last descendant of Caesar, the new emperor [[Galba]] adopted the name of ''Servius Galba Caesar Augustus'', thus making it part of the imperial title. Five days before his murder he adopted [[Lucius Calpurnius Piso Frugi Licinianus|Piso Licinianus]] as his son and heir, renaming him as ''Servius Sulpicius Galba Caesar''.<ref>{{Cite book |last=Harriet I. Flower |title=The Art of Forgetting: Disgrace & Oblivion in Roman Political Culture |publisher=Univ of North Carolina Press |date=2006 |isbn=978-0-8078-3063-5 |page=[https://books.google.com/books?id=4T6Oyezn_msC&pg=PA225 225]}}</ref> After this ''Caesar'' came to denote the heir apparent, who would add the name to his own as heir and retain it upon accession as ''augustus''.{{Sfn|Greenidge|1901|pp=352–355}} The only emperor not to assume it was [[Vitellius]], who adopted the name ''Germanicus'' instead. Most emperors used it as their ''nomen'' – with ''Imperator'' as their ''praenomen'' – until the reign of [[Antoninus Pius]], when it permanently became part of the formula ''Imperator Caesar'' [full name] ''Augustus''.{{Sfn|Hammond|1957}} In the 3rd century, ''caesars'' also received the honorific of ''[[nobilissimus]]'' ("most noble"), which later evolved into a separate title.<ref>{{Cite book |last=Bury |first=J. B. |title=The Imperial Administrative System in the Ninth Century |date=2015 |publisher=Cambridge University Press |isbn=978-1-1080-8150-4 |page=[https://books.google.com/books?id=c7-wBgAAQBAJ&pg=PA35 35]}}</ref>

[[File:INC-3055-a Ауреус. Констанций II. Ок. 355—361 гг. (аверс).png|thumb|200x200px|Coin of [[Constantius II]] marked: {{Smallcaps|d(ominus) n(oster) constantius p(ius) f(elix) aug(ustus)}}]]
During the [[Tetrarchy]] the powers of the ''caesar'' increased considerably, but following the accession of [[Constantine I]] it once more remained as a title for heirs with no significant power attached to it. The title slowly lost importance in the following decades, as emperors started to promote their sons directly to ''augustus''. In the East, the title finally lost its imperial character in 705, when [[Justinian II]] awarded it to [[Tervel of Bulgaria]].{{Efn|''Kaisar'' was originally a common way of referring to the emperor in the East. By the 6th-century, however, writers considered it to be a lower title than ''basileus''.<ref name=Wif/>}} After this it became a court title bestowed to prominent figures of the government, and lost even more relevance after the creation of the title ''[[sebastokrator]]'' by [[Alexios I Komnenos]].{{Sfn|Kazhdan|1991|p=363}} Despite this, its regular use by earlier emperors led to the name becoming synonym with "emperor" in certain regions. Several countries use ''Caesar'' as the origin of their word for "emperor", like ''[[Kaiser]]'' in [[German Empire|Germany]] and ''[[Tsar]]'' in [[First Bulgarian Empire|Bulgaria]] and [[Russia]].

After the [[Constantinian dynasty]], emperors followed ''Imperator Caesar'' with ''[[Flavius]]'', which also began as a family name but was later incorporated into the emperor's titles, thus becoming ''Imperator Caesar Flavius''.<ref>{{Cite book |last=Rösch |first=Gerhard |title=Onoma Basileias |publisher=Verlag der österreichischen Akademie der Wissenschaften |date=1978 |isbn=978-3-7001-0260-1 |series=Byzantina et Neograeca Vindobonensia |pages=49–50 |language=de}}</ref> The last use of the formula, rendered as ''Autokrator Kaisar Flabios... Augoustos'' (Αὐτοκράτωρ καῖσαρ Φλάβιος αὐγουστος) in Greek, is in the ''[[Basilika]]'' of [[Leo VI the Wise]] ({{R.|886|912}}).<ref>Novela 1, in ''Jus Graeco-Romanum'' III, p. [https://books.google.com/books?id=-54UAAAAYAAJ&pg=PA67 67].</ref>

===''Augustus''===
{{Main|Augustus (title)}}

Originally the main title of the emperor.<ref>{{Harvnb|Loewenstein|1973|p=349}}; {{Cite journal |last=Strothmann |first=Meret (Bochum) |date=2006-10-01 |title=Augustus [2] |url=https://referenceworks.brillonline.com/entries/brill-s-new-pauly/augustus-2-e12220040# |journal=Brill's New Pauly}}</ref> According to [[Suetonius]], it was "not merely a new title but a more honorable one, inasmuch as sacred places too, and those in which anything is consecrated by augural rites are called "august" (''augusta''), from the increase (''auctus'') in dignity". It was also connected to the religious practice of [[augury]], which was itself linked to Rome's founding by [[Romulus]], and to ''[[auctoritas]]'', the authority based on prestige.<ref>[https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Suetonius/12Caesars/Augustus*.html# Suetonius, ''Augustus'' 7.]; {{Cite book |last=Southern |first=Patricia |title=Augustus |date=2013 |publisher=Routledge |isbn=978-1-1345-8949-4 |page=[https://books.google.com/books?id=9QsiAQAAQBAJ&pg=PA196 196]}}</ref> The honorific was awarded as both a name and a title to Octavian in 27 BC and was inherited by all subsequent emperors, who placed it after their personal names. The only emperor to not immediately assume it was [[Vitellius]], although he did use it after his recognition by the Senate.<ref>[[Tacitus]]. ''[[Annals (Tacitus)|Annals]]'', [[wikisource:The Histories (Tacitus)/Book 2|Book II, 62, 90]].</ref> Later emperors ruled alongside one or several junior ''augusti'' who held ''[[de jure]]'' (but not ''[[de facto]]'') equal constitutional power.{{Efn|Initially the number of co-emperors was often no more than one. [[Constantine I]] notably ruled alongside eight successive emperors of equal seniority (perhaps with the exception of [[Valerius Valens]] and [[Martinian (emperor)|Martinian]]).}} Despite its use as the highest imperial title, it was generally not used to indicate the office of ''Emperor'' itself, as ordinary people and writers had become accustomed to ''Imperator''.

In the East the title was initially translated as ''[[Sebastos]]'', but the form ''Augoustos'' eventually became more common. Emperors after [[Heraclius]] styled themselves as ''[[Basileus]]'', but ''Augoustos'' still remained in use in a lesser form up until the end of the Empire. In the West, the title was also used by Charlemagne and the subsequent Holy Roman Emperors as part of the formula ''Imperator Augustus''. Both Eastern and Western rulers also used the style ''semper augustus'' ("forever augustus").<ref>{{Cite book |last=Drocourt |first=Nicolas |title=A Companion to Byzantium and the West, 900–1204 |date=2021 |publisher=Brill |isbn=978-9-0044-9924-9 |page=[https://books.google.com/books?id=df1TEAAAQBAJ&pg=PA234 234]}}</ref>

===''Princeps''===
{{Main|Princeps}}

The word ''princeps'', meaning "first", was a republican term used to denote the leading member of the Senate, and it was used by the early emperors to emphasize the continuance of the Republic.{{Sfn|Greenidge|1901|pp=352–355}} The title had already been used by [[Pompey]] and [[Julius Caesar]], among others. It was a purely honorific title with no attached duties or powers, hence why it was never used in official titulature.<ref>{{Cite book |last=Salmon |first=Edward Togo |title=A History of the Roman World from 30 B.C. to A.D. 138 |date=1968 |publisher=Psychology Press |isbn=978-0-4150-4504-9 |page=[https://books.google.com/books?id=jzOSdHYWML4C&pg=PA11 11]}}; {{Harvnb|Greenidge|1901|pp=352–355}}.</ref> The title was the most preferred by Augustus as its use implies only "primacy" (is in the "[[first among equals]]"), as opposed to ''dominus'', which implies dominance. It was the title used by early writers before the term ''imperator'' became popular.<ref name="Paterculus81">[[Paterculus]] ([https://penelope.uchicago.edu/Thayer/L/Roman/Texts/Velleius_Paterculus/2C*.html#81 II, 80–90]), for example, only uses ''princeps'', but the English text translates the word directly as "emperor". [[Livy]] ([https://la.wikisource.org/wiki/Ab_Urbe_Condita/liber_I#19 I. 19]) calls Augustus ''imperator'' once, but he also uses the term when writing about other generals ([https://la.wikisource.org/wiki/Ab_Urbe_Condita/liber_II II. 39ff]).</ref> In his ''[[Res Gestae Divi Augusti|Res Gestae]]'', Augustus explicitly refers to himself as the ''[[princeps senatus]]''.<ref>''[[Res Gestae Divi Augusti|Res Gestae]]'' [https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Augustus/Res_Gestae/1*.html# I.7], "For ten years in succession I was one of the triumvirs for the re-establishment of the constitution. To the day of writing this [June/July AD&nbsp;14] I have been ''[[princeps senatus]]'' for forty years." Augustus thus dates his tenure as ''princeps'' from 27&nbsp;BC. He also only counts his ''[[de jure]]'' tenure as triumvir.</ref> The title was also sometimes given to heirs, in the form of ''[[princeps iuventutis]]'' ("first of the youth"), a term that continued to be used during the [[Tetrarchy]].<ref>{{Cite book |last=Rees |first=Roger |title=Layers of Loyalty in Latin Panegyric, AD 289–307 |date=2002 |publisher=Oxford University Press |isbn=978-0-1992-4918-3 |pages=[https://books.google.com/books?id=LQQ5Ce-2de4C&pg=PA146 146]–147}}</ref>

In the era of Diocletian and beyond, ''princeps'' fell into disuse and was replaced with ''dominus'' ("lord");{{Sfn|Goldsworthy|2010|p=443}} the use of ''princeps'' and ''dominus'' broadly symbolizes the differences in the empire's government, giving rise to the era designations [[Principate]] and [[Dominate]]. The title is still found in some later sources, however. The poet [[Claudian]], for example, describes [[Honorius (emperor)|Honorius]] as having been raised from "''caesar''" to "''princeps''" (instead of ''augustus'').{{Sfn|Hekster|2022|p=42}} The title survived the [[fall of the Western Roman Empire]], as it was used by rulers such as [[Theodoric the Great]].

[[File:Solidus of Leo VI (reverse).jpg|thumb|Coin of [[Leo VI the Wise|Leo VI]] ({{R.|886|912}}) marked: {{Smallcaps|leon en cristo basileus romaeon}}]]

=== ''Basileus'' / ''autokrator'' ===
{{Main|Basileus}}
''Basileus'' was the traditional Greek title for monarchs. It was first used by [[Alexander the Great]] ({{R.|336|323}} BC) during his conquests.<ref>{{Cite book |last1=Roisman |first1=Joseph |title=A Companion to Ancient Macedonia |last2=Worthington |first2=Ian |date=2010 |publisher=John Wiley & Sons |isbn=978-1-4051-7936-2 |page=[https://books.google.com/books?id=lkYFVJ3U-BIC&pg=PA375 375]}}</ref> The term was applied to emperors unofficially since the beginning of the Empire,{{Sfn|Bury|2012|pp=15–16}} but in official records it was often used as the Greek translation of the title ''[[Rex (title)|rex]]'', with ''[[autokrator]]'' (the Greek equivalent to ''[[imperator]]'') reserved for the emperor. As a result, Western writers often associated ''basileus'' with "king" as opposed to "emperor", despite this distinction not existing in Greek.<ref>{{Cite book |last=Madariaga |first=Isabel De |title=Politics and Culture in Eighteenth-Century Russia |date=2014 |publisher=Routledge |isbn=978-1-3178-8190-2 |pages=[https://books.google.com/books?id=omjXAwAAQBAJ&pg=PA17 17]–18}}</ref>

''Basileus'' was first officially used by [[Heraclius]] in 629, after his [[Byzantine–Sasanian War of 602–628|victory over the Persians]], and it became the main title of the emperor afterward. After the 9th century, the full imperial title became "''basileus'' and ''autokrator'' of the Romans" (βασιλεύς καὶ αὐτοκράτωρ Ῥωμαίων), with ''autokrator'' distinguishing the senior emperor of the junior ''basileus''.{{Sfn|Kazhdan|1991|p=235}} In later centuries, the title was shortened simply as "''autokrator'' of the Romans", resulting in a revival of that title.<ref>{{Cite book |last1=Bellinger |first1=Alfred Raymond |title=Catalogue of the Byzantine Coins in the Dumbarton Oaks Collection and in the Whittemore Collection |last2=Grierson |first2=Philip |date=1973 |publisher=Dumbarton Oaks |isbn=978-0-8840-2261-9 |page=[https://books.google.com/books?id=NJmoF52BiBsC&pg=PA96 96]}}</ref> In later centuries, an emperor would typically be acclaimed as ''basileus'' as an infant and then [[Coronation of the Byzantine emperor|crowned by the Patriarch]] as ''autokrator''.<ref name="RuthMacrides"/> Foreign rulers were usually referred to as ''reges'' (a Greek rendition of ''rex''), but the Eastern emperors were eventually forced to recognize other monarchs as ''basileus'', mainly the [[Latin Emperor|Latin]],<ref>{{Cite book |last=Tricht |first=Filip Van |title=The Latin Renovatio of Byzantium: The Empire of Constantinople (1204–1228) |date=2011 |publisher=Brill |isbn=978-9-0042-0392-1 |pages=[https://books.google.com/books?id=KOJ5DwAAQBAJ&pg=PA357 357]}}</ref> [[Holy Roman Emperor|Holy Roman]], [[List of Serbian monarchs|Serbian]] and [[List of Bulgarian monarchs|Bulgarian emperors]].{{Sfn|Kazhdan|1991|p=235}}

==Later assertions to the title==
{{Main|Succession of the Roman Empire|Succession to the Byzantine Empire}}Despite overthrowing Roman rule, [[Odoacer]] never claimed the imperial dignity. His successor [[Theodoric the Great]] is sometimes said to have been an emperor in all but name, despite using the title of ''[[Rex (title)|rex]]'' and recognizing the emperor in Constantinople. He also used the ancient title of ''[[princeps]]'' (in full, ''princeps Romanus'') and ''dominus noster'', actively trying to imitate the old emperors.{{Efn|There is one inscription (erected by a senator and not Theoderic himself) that calls him ''augustus'', which may indicate that some of his subjects regarded him as an emperor. [[Procopius]] refers to him as a "genuine emperor" (''basileus'') despite being "in name an usurper" (''tyrannos'').<ref name="pat"/>}}<ref name="pat">{{Cite book |last=Amory |first=Patrick |title=People and Identity in Ostrogothic Italy, 489–554 |date=2003 |publisher=Cambridge University Press |isbn=978-0-5215-2635-7 |pages=[https://books.google.com/books?id=7ndeDi_fwq0C&pg=PA59 59]}}</ref><ref>{{Cite book |last1=Fouracre |first1=Paul |title=The New Cambridge Medieval History: Volume 1, c. 500–c. 700 |last2=McKitterick |first2=Rosamond |last3=Abulafia |first3=David |date=1995 |publisher=Cambridge University Press |isbn=978-0-5213-6291-7 |page=[https://books.google.com/books?id=JcmwuoTsKO0C&pg=PA146 146]}}</ref> He even requested and received the [[regalia]] sent to Constantinople by Odoacer, although it appears that he only requested the purple robes and not the imperial crown nor scepter.<ref>{{Cite book |last=Arnold |first=Jonathan J. |title=Theoderic and the Roman Imperial Restoration |date=2014 |publisher=Cambridge University Press |isbn=978-1-1070-5440-0 |pages=[https://books.google.com/books?id=WOWfAgAAQBAJ&pg=PA75 72–77], 100–104}}</ref>

The rebels [[Burdunellus]] and [[Peter (usurper)|Peter]], both active shortly after the fall of the West, are referred to as "tyrants" in sources. This may imply that they claimed the imperial dignity, although there is almost no information available for these rebellions.<ref>{{Cite book |last=Collins |first=Roger |title=Visigothic Spain 409–711 |date=2008 |publisher=John Wiley & Sons |isbn=978-0-4707-5456-6 |pages=[https://books.google.com/books?id=WlSu_iWzA9AC&pg=PA35 35–36]}}</ref> The [[Berbers|Berber]] governor [[Masties]] assumed the title of ''imperator'' shortly after 476, claiming to rule over the "Romans and Maurians."<ref>{{Citation |last=Martindale |first=John R. |title=''Masties''. The Prosopography of the Later Roman Empire – Volume 2 |page=[https://books.google.com/books?id=G5W6vCO_pYUC&pg=PA734 734] |date=1980 |publisher=Cambridge University Press |isbn=0-5212-0159-4}}</ref> The last attempt to restore the office of emperor in the West was during the [[Siege of Ravenna (539–540)]], when the Goths offered [[Belisarius]] the throne, which he refused.<ref>{{Cite book |last=Moorhead |first=John |title=Justinian |date=2013 |publisher=Routledge |isbn=978-1-3178-9879-5 |page=[https://books.google.com/books?id=sKYuAgAAQBAJ&pg=PA85 85]}}</ref>

==Number of emperors==

[[File:07 constantius2Chrono354.png|thumb|right|295x295px|Portrait of [[Constantius II]] in [[Filocalus]]'s [[Chronograph of 354]]]]Several ancient writers tried to count the number of Roman emperors through history, but each of them gives a different count. The 4th-century historian [[Festus (historian)|Festus]] states that "From [[Augustus|Octavian Caesar Augustus]] to [[Jovian (emperor)|Jovian]], there were ''imperatores'', 43 in number, through 407 years [reckoning from [[43 BC]]]".<ref>[https://web.archive.org/web/20220422150556/http://www.roman-emperors.org/festus.htm Breviarum] in ''[[De Imperatoribus Romanis]]''.</ref> The 6th-century ''[[Chronicon Paschale]]'' calls [[Diocletian]] the "33rd Roman emperor". Adding the eight other emperors mentioned in the work would give a total of 41 emperors up until [[Constantine I]].<ref name="cp">''[[Chronicon Paschale]]'' [https://archive.org/details/chronicon-p/page/n33/mode/2up?view=theater Olympiads 266–276]</ref>

A few writers also attempted to make their own lists of emperors. The 4th-century calligrapher [[Furius Dionysius Filocalus|Filocalus]], in his [[Chronograph of 354|''Chronographia'']], records 58 emperors from Augustus to Constantine.<ref>[https://www.tertullian.org/fathers/chronography_of_354_16_chronicle_of_the_city_of_rome.htm Chronography of 354 AD. Part 16: Chronicle of the City of Rome]. ''[[Tertullian]].org''.</ref> His contemporary [[Epiphanius of Salamis|Epiphanius]] records 44 emperors in his work ''[[On Weights and Measures]]''.<ref>{{Cite book |last=Dean |first=James Elmer |url=https://oi.uchicago.edu/research/publications/saoc/saoc-11-epiphanius%E2%80%99-treatise-weights-and-measures-syriac-version |title=Epiphanius' Treatise on Weights and Measures: The Syriac Version |publisher=The University of Chicago Press |date=1935 |pages=28–39 |oclc=912074}}</ref> The 13th-century ''[[Chronicon Altinate]]'' records 46 emperors in the same time period.<ref>[[Roberto Cessi|Cessi, Roberto]], ed. (1993). [http://asa.archiviostudiadriatici.it/islandora/object/libria%3A209776#page/160/mode/2up ''Origo civitatum Italie seu Venetiarum (Chronicon Altinate et Chronicon Gradense)'']. Tipografia del senato. pp. 102–104. {{OCLC|1067434891}}</ref> These discrepancies arise from the fact that there was never a defining distinction between "legitimate emperors" and "[[Roman usurper|usurpers]]".{{Sfn|Omissi|2018|pp=3–33}} Other emperors had such uneventful or brief reigns that they are unmentioned by literary sources, like Licinius's co-emperors [[Valerius Valens]] and [[Martinian (emperor)|Martinian]].<ref>{{Cite book |last=Barnes |first=Timothy D. |title=The New Empire of Diocletian and Constantine |date=1982 |isbn=978-0-6742-8066-3 |page=15 |doi=10.4159/harvard.9780674280670 |quote=Literary sources explicitly style him Caesar, the coins Augustus}}</ref>

==See also==
{{Portal|Ancient Rome}}
* [[List of Roman emperors]]
* [[List of Roman empresses]]
* [[List of condemned Roman emperors]]
* [[List of Roman imperial victory titles]]
* [[List of Italian monarchs]]
* [[List of Roman usurpers]]
* [[Family tree of Roman emperors]]
* [[Roman imperial cult]]
* [[Roman usurper]]

==Notes==
{{Notelist}}

== References ==
=== Citations ===
{{Reflist|30em}}

=== Sources ===
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* {{Cite book |last=Barnes |first=Timothy |title=A Companion to Julius Caesar |date=2009 |publisher=[[John Wiley & Sons]] |isbn=978-1-4443-0845-7 |editor-last=Griffin |editor-first=Miriam |chapter=The first Emperor: the view of late antiquity |chapter-url=https://books.google.com/books?id=gzOXLGbIIYwC}}
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{{Refend}}

==Further reading==
{{Refbegin|30em}}
* {{Cite book |last=Ágoston |first=Gábor |url=https://books.google.com/books?id=kXALEAAAQBAJ |title=The Last Muslim Conquest |date=2021 |publisher=Princeton University Press |isbn=978-0-6911-5932-4 |location=Princeton}}
* {{Cite book |last=Christoforou |first=Panayiotis |title=Imagining the Roman Emperor: perceptions of rulers in the high empire. |date=2023 |publisher=Cambridge University Press |isbn=978-1-0093-6249-8 |location=Cambridge}}
* {{Cite book |last=Çolak |first=Hasan |title=Frontiers of the Ottoman Imagination: Studies in Honour of Rhoads Murphey |date=2014 |publisher=Brill |isbn=978-9-0042-8351-0 |editor-last=Hadjianastasis |editor-first=Marios |location=Leiden |chapter=''Tekfur'', ''fasiliyus'' and ''kayser'': Disdain, Negligence and Appropriation of Byzantine Imperial Titulature in the Ottoman World |chapter-url=https://brill.com/view/book/edcoll/9789004283510/B9789004283510_003.xml}}
* {{Cite book |last=Enepekides |first=P. K. |title=Akten des 11. Internat. Byzantinisten-Kongresses 1958 |date=1960 |publisher=C.H. Beck |location=Munich |pages=138–143 |language=de |chapter=Das Wiener Testament des Andreas Palaiologos vom 7. April 1502 |trans-chapter=The Vienna Testament of Andreas Palaiologos from 7 April 1502 |oclc=761003148}}
* {{Cite book |last=Freiberg |first=Jack |url=https://books.google.com/books?id=X760BAAAQBAJ&q=Constantinople |title=Bramante's Tempietto, the Roman Renaissance, and the Spanish Crown |date=2014 |publisher=Cambridge University Press |isbn=978-1-1070-4297-1 |location=New York}}
* {{Cite book |last=Kumar |first=Krishan |url=https://books.google.com/books?id=q8iXDwAAQBAJ |title=Visions of Empire: How Five Imperial Regimes Shaped the World |date=2017 |publisher=Princeton University Press |isbn=978-0-6911-9280-2 |location=Princeton}}
* {{Cite book |last=Millar |first=Fergus |url=https://books.google.com/books?id=E57tAAAAMAAJ |title=The Emperor in the Roman World, 31 BC–AD 337 |date=1977 |publisher=Cornell University Press |isbn=978-0-8014-1058-1}}
* {{Cite book |last=Moustakas |first=Konstantinos |url=https://books.google.com/books?id=qnHPfZ7mr4YC |title=Images of the Byzantine World: Visions, Messages and Meanings : Studies Presented to Leslie Brubaker |date=2011 |publisher=Ashgate |isbn=978-1-4094-0776-8 |editor-last=Lymberopoulou |editor-first=Angeliki |location=Farnham |chapter=Byzantine 'Visions' of the Ottoman Empire: Theories of Ottoman Legitimacy by Byzantine Scholars after the Fall of Constantinople}}
* {{Cite journal |last=Nicol |first=Donald M. |author-link=Donald Nicol |date=1967 |title=The Byzantine View of Western Europe |journal=Greek, Roman and Byzantine Studies |volume=8 |issue=4 |pages=315–339}}
* {{Cite book |last=Nicol |first=Donald M. |author-link=Donald Nicol |title=The Immortal Emperor: The Life and Legend of Constantine Palaiologos, Last Emperor of the Romans |date=1992 |publisher=Cambridge University Press |isbn=978-0-5115-8369-8 |location=Cambridge}}
* {{Cite book |last1=Nicolle |first1=David |title=The Fall of Constantinople: The Ottoman Conquest of Byzantium |last2=Haldon |first2=John |last3=Turnbull |first3=Stephen |date=2007 |publisher=Osprey Publishing |isbn=978-1-8460-3200-4 |oclc=78989635}}
* {{Cite book |last=Ostrogorsky |first=George |url=https://archive.org/details/historyofbyzanti0000unse |title=History of the Byzantine State |date=1957 |publisher=[[Rutgers University Press]] |location=New Brunswick |translator-last=Hussey |translator-first=Joan}}
* Scarre, Chris. ''Chronicle of the Roman Emperors: The Reign-by-Reign Record of the Rulers of Imperial Rome''. London: Thames & Hudson, 1995. {{ISBN|0-5000-5077-5}}
* {{The Papacy and the Levant |volume=2}} <!-- Setton -->
* {{Cite journal |last=Wallace-Hadrill |first=Andrew |date=1982 |title=Civilis Princeps: Between Citizen and King |journal=The Journal of Roman Studies |volume=72 |pages=32–48 |doi=10.2307/299114 |issn=0075-4358 |jstor=299114 |s2cid=162347650}}
* {{Cite book |last=Üre |first=Pinar |title=Reclaiming Byzantium: Russia, Turkey and the Archaeological Claim to the Middle East in the 19th Century |date=2020 |publisher=I. B. Tauris |isbn=978-1-7883-1012-3 |location=London}}
{{Refend}}

==External links==
* [https://web.archive.org/web/20220402152802/http://www.roman-emperors.org/startup.htm Website] of ''[[De Imperatoribus Romanis]]''
* [http://www.friesian.com/decdenc1.htm Decadence, Rome and Romania, and the Emperors Who Weren't, and Other Reflections on Roman History], by Kelley L. Ross

{{Epochs of Roman Emperors}}
{{Roman emperors}}
{{Ancient Rome topics}}

[[Category:20s BC establishments in the Roman Empire]]
[[Category:1453 disestablishments]]
[[Category:15th-century disestablishments in the Byzantine Empire]]
[[Category:Roman emperors| ]]
[[Category:Ancient Roman titles|Emperor, Roman]]
[[Category:Positions of authority]]