The Roman Empire lasted longer than most empires. It lasted from the republic in 509 BCE to the fourth century CE when Rome was sacked for the last time by Germanic and Arab tribes (although some Roman emperors continued on as figureheads in Constantinople for centuries).
More than one emperor spent his entire life trying to revive it again, but none could. Even if they could, they just weren’t Romans anymore. The people who ceased being “Romans” were the invaders or anyone who settled there after 390 AD; these weren’t members of that proud civilization founded by Aeneas and started by Romulus and Remus long before Athens hailed them with disdain or that young city had even heard their story…