List of Roman emperors

Roman Emperors were rulers of the Roman Empire, wielding power over its citizens and military. The empire was developed as the Roman Republic invaded and occupied most 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". Rome and its senate were ruled by a variety of magistrates – of whom the consuls were the most powerful. The republic ended, and the emperors were created, when these magistrates became legally and practically subservient to one citizen with power over all other magistrates. Augustus, the first emperor, was careful to maintain the facade of republican rule, taking no specific title for his position and calling the concentration of magisterial power Princeps Senatus (the first man of the senate). This style of government lasted for 300 years, and is thus called the Principate era. 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, it still had to be earned by the 'Princeps'. The term emperor is a modern construction, used when describing rulers of the Roman Empire because it emphasises the strong links between the ruler and the army (on whose support the ruler's power depended), and does not discriminate between the personal styles of rule and titles in different phases of the Empire.

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 experiment with sharing imperial titles and responsibilities among several individuals - a partial reversion to pre-Augustian Roman traditions. For nearly two centuries thereafter there was often more than one emperor at a time, frequently dividing the administration of the vast territories between them. As Henry Moss warned, "Yet it is important to remember that in the eyes of contemporaries the Empire was still one and indivisible. It is false to the ideas of this time to speak of 'the Eastern and Western Empire'; the two halves of Empire were thought of as 'the Eastern, or Western parts' (partes orientis vel occidentis.)" However, after the death of Theodosius I (395), the split became firmly entrenched (see: Western and Eastern) The last pretense of such division was formally ended by Zeno after the death of Julius Nepos in 480. For the remaining thousand years of eastern Roman history there would only ever be one legitimate senior emperor, ruling from Constantinople and maintaining claim to the increasingly unstable territories in the west. After 480, multiple claims to be the imperial title of Augustus (or Basileus for Greek speakers) necessarily meant civil war, although the experiment with designating junior emperors (called now Caesars), usually to indicate the intended successor, occasionally reappeared.

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