[Dormant] moved to !roughromanmemes@piefed.social

I would argue that the Empire as an imperialist hegemon started with their conquests that formed a hegemony, which I'd place around 340 BCE. The Principate replaced the Republic in 27 BCE with the ascension of Octavian, later to he replaced by the Dominate in 284 BCE with the ascension of Diocletian(though that distinction is disputed), together forming the Empire as a system dominated by the reigns of Emperors, ended as you describe by the deposition of Romulus Augustus in 476 CE and the conquest of Constantinople in 1453 CE.