A Roman emperor was the sole ruler of the Roman state. Historians usually count Augustus as the first, from 27 BC. Emperors held supreme command of the army and wide powers over the law, and ruled for as long as they kept the army's support.
Key takeaways
- Modern historians count Augustus, who received that title in 27 BC, as the first emperor, though the date is partly symbolic [1].
- There was no fixed rule of succession: emperors usually adopted an heir, and the army was the real basis of their power [1].
- On the map, AD 14 is the first handover of power from one emperor to the next: Augustus dies; Tiberius succeeds.
- The Western line of emperors ended in AD 476, and the Eastern line in AD 1453 [1].
How a Roman emperor held power
Rome had no word for "emperor" that meant what we mean by it. The English word comes from imperator, a title that began as an honour given to a successful general [2]. In the Republic power was shared among elected officials such as consuls. Over the first century BC that broke down in civil wars, and the winner, Octavian, was given the title Augustus by the Senate in 27 BC, together with the title princeps ("foremost") and a command over the provinces [2]. Modern historians date the empire from then, though they call it a mostly symbolic date, since the Republic had effectively ended earlier. Many ancient writers thought Julius Caesar was the first emperor [1].
Augustus was careful to say the Republic still existed. The system he built is called the Principate, and its holders used the title princeps to suggest that nothing had really changed [1]. In practice the emperor held imperium maius, supreme command including control of all troops, and tribunicia potestas, the powers of a tribune, including a veto and the right to call the Senate to meet [1]. He could also hold other offices, such as consul, and he was the chief priest, pontifex maximus [1]. A law made for Vespasian said the emperor was "not bound by laws" [1].
There was no clear rule of succession. Emperors normally adopted their chosen heirs. The Senate sometimes confirmed or proclaimed a new emperor, as with Tiberius and Nerva, but the army was the real basis of imperial power [1]. Many emperors began as rebels, and succession crises and civil wars became frequent from AD 192 onward [1]. The Eastern line of emperors continued at Constantinople until the city fell in 1453 [1].
An example from our data
The map's date slider follows the emperors through their handovers. At AD 14: Augustus dies; Tiberius succeeds. The empire then covered 3.67 million km², with 36 provinces held. The AD 14 page shows that moment.
At AD 117: The empire at its greatest extent, after Trajan's eastern conquests; Trajan dies and Hadrian succeeds. The area was then 4.88 million km², the peak on our slider, and the AD 117 page has the detail. Later changes at the top are on the slider too: at AD 211, Septimius Severus dies; his sons Caracalla and Geta succeed, and at AD 395, Theodosius I dies; the empire is divided permanently between his sons.
The end of the line in the West is on the AD 476 page: Odoacer deposes Romulus Augustulus; the Western empire ends, the East continues. The Eastern emperors carried on, and their story is told on the Byzantine Empire page. At the last date on the slider, AD 1453, Constantinople falls to the Ottomans, and the area has shrunk to 22,624 km². The homepage section on why it fell twice gives the wider picture.
The thing people get wrong
Many people assume the empire began on a single day, with a coronation, a crown and a title. In fact Augustus took power step by step, and kept the old titles and offices going. Historians treat 27 BC as a marker, not as a moment when everyone woke up in a new kind of state [1]. The Senate still met, consuls were still elected, and the men of Rome could tell themselves the Republic carried on.
Another mistake is to think emperors inherited by blood. Adoption was common, and many emperors came to the throne through the army or a civil war [1].
Frequently asked questions
Who was the first Roman emperor?
Augustus, in the view of most modern historians. He was given that title in 27 BC. Some ancient writers thought Julius Caesar was the first.
Did the Senate choose the emperor?
Sometimes it confirmed or proclaimed one, as with Tiberius and Nerva, but the army was the real basis of an emperor's power.
Were emperors called emperor?
Not at first. Augustus liked to be called princeps, meaning first citizen. The word emperor comes from imperator, a title of military command.
Sources
- Roman emperor, Wikipedia.
- Roman Empire, Wikipedia.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against Ancient World Mapping Center outlines and Pleiades).