According to the popular conciousness, the Roman Empire lasted from 27 BCE to 476 CE in the west (i.e. 503 years), and from 27 BCE to 1453 CE including Byzantiu

According to the popular conciousness, the Roman Empire lasted from 27 BCE to 476 CE in the west (i.e. 503 years), and from 27 BCE to 1453 CE including Byzantium (i.e. 1480 years). But that's a really bad way to think about it. A Roman in 30 BCE and 20 BC probably wouldn't notice much difference. There was still a Senate, still elections, still powerful men exerting massive influence over the lives of ordinary people. Essentially someone had just written 'Augustus' in chalk at the top of all the organization charts. Similarly, in the west a Roman in 470 CE and 480 CE wouldn't have noticed much difference. There was still a Senate, and powerful 'barbarian' generals were still exerting massive influence over the lives of ordinary people. There even was still an Emperor who was nominally in charge - he was in Constantinople, but the Emperors hadn't lived in Rome for decades. The fall of Constantinople was probably a bit different since a whole new political regieme was imposed, but even there I believe the Ottomans actually claimed to be the inheritors of Rome and the rightful emperors (Rome was Pagan, then Christian, why couldn't it now be Muslim?) Realistically, there were a series of political regimes which evolved into each other time: * Aristocratic Republic, * 'Constitutional' Monarchy, * Absolute Monarchy, * Military Dictatorship, * Theocratic Dictatorship.