I'm a part-time history scholar but Rome is not my focus. However I'd throw the following dates into the mix: 264 BC (start of the Punic Wars) Roman Republic c

I'm a part-time history scholar but Rome is not my focus. However I'd throw the following dates into the mix: 264 BC (start of the Punic Wars) Roman Republic controls the Italian peninsula (as far north as Pisa) and is militarily aggressive 146 BC: Roman Republic dominates the Italian peninsula, has subdued the Greek mainland and razed Carthage 44-15 BC the transition from Republic to Empire 476 AD Western Roman Empire collapses. 1025 AD Eastern/Greek/Byzantine Empire is still a significant power 1204 AD Sack of Constantinople It's hard to say exactly how long they were a power. Behaviorally, they were a strong, aggressive power for 250 years before becoming an Empire. And they were a significant power for 1000 years after losing Rome. So for over 1500 years they were an important state in the Mediterranean. You've got a good point that major events we think of when we say Roman Empire occur in a fairly short span, but I think it's quite accurate to say "The Roman Empire last[ed] the better part of a thousand years" So I think it's fair to say the Roman Empire lasted 1000 years.