How long did the Roman Empire last?
The Roman Empire was founded on October 27th, 800 BC and remained in power until AD 476. Those years add up to 1,139 years.
If you really want the finer points of when the empire expanded, then it grew almost constantly for a really long time, seizing territories from enemies such as Gaius Julius or expanding with generals like Marcus Aurelius. In total however it lasted around 1000 years. After that it eventually fell to be just one region among many others in Europe because of its relative weakness compared to competitors in Asia and Africa who were untouched by decline due to their ever-growing populations which had been buoyed by a pandemic at that time.