List of Roman emperors
The Roman emperors were the rulers of the Roman Empire dating from the granting of the title of Augustus to Gaius Julius Caesar Octavianus by the Roman Senate in 27 BC, after major roles played by the populist dictator and military leader Julius Caesar. Augustus maintained a facade of Republican rule, rejecting monarchical titles but calling himself princeps senatus (first man of the council) and princeps civitatis (first citizen of the state). The title of Augustus was conferred on his successors to the imperial position. The style of government instituted by Augustus is called the Principate and continued until reforms by Diocletian. The modern word 'emperor' derives from the title imperator, which was granted by an army to a successful general; during the initial phase of the empire, the title was generally used only by the princeps. For example, Augustus' official name was Imperator Caesar Divi Filius Augustus.
The territory under command of the emperor had developed under the period of the Roman Republic as it invaded and occupied much of Europe and portions of northern Africa and western Asia. Under the republic, regions of the empire were ruled by provincial governors answerable to and authorised by the Senate and People of Rome. During the republic, the chief magistrates of Rome were two consuls elected each year; consuls continued to be elected in the imperial period, but their authority was subservient to that of the emperor, and the election was controlled by the emperor.
In the late 3rd century, after the Crisis of the Third Century, Diocletian formalised and embellished the recent manner of imperial rule, establishing the so-called Dominate period of the Roman Empire. This was characterised by the explicit increase of authority in the person of the emperor, and the use of the style dominus noster 'our lord'. The rise of powerful Barbarian tribes along the borders of the empire and the challenge they posed to defense of far-flung borders and unstable imperial succession led Diocletian to divide the administration geographically of the Empire in 286 with a co-Augustus.
In 313, Constantine the Great, the first Christian emperor, issued the Edict of Milan along with Licinius that granted freedom in the worship of Christianity. In 330, he established a second capital in Byzantium, which he renamed Constantinople. For most of the period from 286 to 480, there was more than one recognised senior emperor, with the division usually based in geographic terms. This division was consistently in place after the death of Theodosius I in 395, which historians have dated as the division between the Western Roman Empire and the Eastern Roman Empire. However, formally the Empire remained a single polity, with separate co-emperors in the separate courts. The fall of the Western Roman Empire, and so the end of a separate list of emperors below, is dated either from the de facto date of 476 when Romulus Augustulus was deposed by the Germanic Herulians led by Odoacer or the de jure date of 480, on the death of Julius Nepos, when Eastern emperor Zeno ended recognition of a separate Western court. In the period that followed, the Empire is usually treated by historians as the Byzantine Empire governed by the Byzantine emperors, although this designation is not used universally, and continues to be a subject of specialist debate today.
In the 7th century reign of Heraclius, the Byzantine–Sasanian War of 602–628 saw much of Rome's eastern territory lost to the Sasanian Empire, recovered by Heraclius, and then lost permanently to Arab Muslim conquests after the death of Muhammad and establishment of Islam. The Sasanian Empire was conquered by the Rashidun Caliphate, ending the Byzantine-Sasanian Wars.
The line of emperors continued until the death of Constantine XI Palaiologos during the Fall of Constantinople in 1453, when the remaining territories were captured by the Ottoman Empire under Mehmed II. The Ottoman dynasty carried on using the title of Caesar of Rome.
Counting all individuals to have possessed the full imperial title, including those who did not technically rule in their own right (e.g. co-emperors or minors during regencies), this list contains 194 emperors and 3 ruling empresses, for a total of 197 monarchs.