How long did the Roman Empire last?

It depends what you count

Rome had a kingdom, a republic and an empire, and the empire ended twice. Here are the usual dates and the arithmetic. One trap first: there is no year zero. The year 1 BC is followed directly by AD 1, so adding the BC and AD numbers counts one year too many.

1. The kingdom, 753–509 BC. Seven kings, by tradition, over 244 years. The founding date is legend, but archaeologists have found huts on the Palatine Hill from around the eighth century BC.
2. The Republic, 509–27 BC. Consuls elected every year instead of kings, for about 480 years.
3. The united empire, 27 BC–AD 395. From Augustus to the death of Theodosius, about 420 years.
4. The western empire, 395–476. Eighty-one more years, until the last emperor in Italy was retired.
5. The eastern empire, 395–1453. More than a thousand years more, ruled from Constantinople.

Add them up and you get about 500 years of empire in the West, nearly 1,500 in the East, and 1,228 years from Romulus to Romulus Augustulus, the last western emperor. From 753 BC to 1453 is 2,205 years.

Why 27 BC?

Rome’s first emperor was never crowned. The change came disguised as its opposite. In January 27 BC Octavian handed his powers back to the Senate, and the Senate gave him a new name.

I transferred the republic from my own control to the will of the senate and the Roman people. For this service on my part I was given the title of Augustus by decree of the senate …

Historians start the empire there because Augustus kept the legions and the treasury for the rest of his life and passed them to his heir. Some prefer 31 BC, the battle of Actium, when his last rival lost. The road from Republic to emperor took a century.

Why 476, and why it is not the end

On 4 September 476 the general Odoacer retired the boy emperor Romulus Augustulus and sent the imperial regalia to Constantinople. Nobody stormed Rome. Later writers, such as Marcellinus Comes around 518, made 476 the turning point. Why the West fell is a long story of its own.

The eastern half simply carried on, with the same laws and the same title, from the capital Constantine had dedicated in 330. Its people called themselves Romans, which is why historians argue over the name Byzantine. It ended on 29 May 1453, when the Ottoman sultan Mehmed II broke the walls of Constantinople.

Counting the Roman way

Romans named each year after its two consuls. Scholars also counted years “from the founding of the city,” ab urbe condita, and in the first century BC the scholar Varro fixed that founding at 753 BC. By his reckoning AD 1 was the year 754. In April 248 the emperor Philip the Arab marked Rome’s thousandth birthday with games that Eutropius calls vastly magnificent.

The name outlived every Roman state. A Greek empire at Trebizond, on the Black Sea, held out until 1461. In the West, Pope Leo III crowned Charlemagne emperor of the Romans in 800, and the Holy Roman Empire that grew out of that title lasted until 1806. Mehmed II himself took the title Caesar of Rome.