Constitution of the late Roman Empire

Politics of ancient Rome
Periods
Roman Kingdom 753–509 BC Roman Republic 509–27 BC Roman Empire 27 BC – AD 395 Principate 27 BC – AD 284 Dominate AD 284–641 Western AD 395–476 Eastern AD 395–1453 Timeline
Constitution
Kingdom Republic Sullan republic Empire Augustan reforms Late Empire
Political institutions
Imperium Collegiality Auctoritas Roman citizenship Cursus honorum
Assemblies
Centuriate Curiate Plebeian Tribal
Ordinary magistrates
Consul Praetor Quaestor Promagistrate Aedile Tribune Censor Governor
Extraordinary magistrates
Corrector Dictator Magister equitum Consular tribune Rex Triumviri Decemviri
Public law
Mos maiorum Ius Senatus consultum Quaestio perpetua Senatus consultum ultimum
Titles and honours
Emperor Legatus Dux Officium Praeses Praefectus Vicarius Vigintisexviri Triumvir monetalis Lictor Magister militum Imperator Princeps senatus Pontifex maximus Augustus Caesar Tetrarch
Other countries
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The constitution of the late Roman Empire was an unwritten set of guidelines and principles passed down, mainly through precedent, which defined the manner in which the late Roman Empire was governed.^[1] As a matter of historical convention, the late Roman Empire emerged from the Roman Principate (the early Roman Empire), with the accession of Diocletian in AD 284, his reign marking the beginning of the Tetrarchy.^[2] The constitution of the Dominate outrightly recognized monarchy as the true source of power, and thus ended the facade of dyarchy, in which emperor and Senate governed the empire together.^[3]

Diocletian's reforms to the Imperial government finally put an end to the period when the old Republican magistracies (e.g. consuls and praetors) held real powers. From then, the consuls had almost no real duties beyond that of presiding at Senate meetings and the duties of the lesser magistrates were effectively just hosting various games, e.g. chariot racing.^[3] Most other lesser magistracies simply disappeared.

Diocletian attempted to reform the Imperial system itself into a structure in which four emperors, consisting of two Augusti and two Caesares, each governed one fourth of the Empire.^[4] Known as the Tetrarchy, this constitutional structure, however, failed to even outlast Diocletian, who lived to see the collapse of his system and the civil wars that followed in his retirement after abdication in AD 305.

He also enacted major administrative reforms to the Empire. His division of the Empire into east and west, with each half under the command of a separate emperor, remained with brief interruptions of political unity.^[5] Although it remained the sole capital until Constantinople was elevated to that status in 359, the city of Rome ceased to be the seat of the Imperial government which in the West was usually in Mediolanum (now Milan), or sometimes in Augusta Treverorum (now Trier) if an emperor was resident there, or wherever the emperor happened to be since 4th century emperors moved within their realms, though Rome still had had its own Praefectus urbi above all other municipal governors and mayors and also its own Senate with Imperial level above all other municipal councils (except that of Constantinople from 359), maintaining the de jure capital status.

A vicar, later two vicars under Praetorian Prefect of Italy, headed the imperial administration of Italy, one in suburbicarian Italy (south of the Apennines and the Islands) and the other in Annonarian Italy (north of the Apennines and Raetia). The Senate and executive magistrates continued to function as Diocletian's constitution had originally specified. Diocletian's civil and military divisions of the empire remained in effect with little change though Upper Egypt from the mid-fifth was governed by a general, the dux, who also exercised civilian authority over the population. Later emperor Constantine would modify Diocletian's constitution^[6] by changing the roles of officials somewhat but not the administrative framework. It was not until Justinian I 527-565 that major changes that saw the near abolition of the regional tier of officials, and severe weakening of the Treasury (sacrae largitones) and Crown Estates.