In practice, Roman society was hierarchical.[2][3] The evolution of the Constitution of the Roman Republic was heavily influenced by the struggle between Rome's land-holding aristocracy (the patricians), who traced their ancestry back to the early history of the Roman kingdom, and the far more numerous citizen-commoners, the plebeians. Over time, the laws that gave Patricians exclusive rights to Rome's highest offices were repealed or weakened, and a new aristocracy emerged from among the plebeian class. The leaders of the Republic developed a strong tradition and morality requiring public service and patronage in peace and war, meaning that military and political success were inextricably linked. During the first two centuries of its existence the Republic expanded through a combination of conquest and alliance, from central Italy to the entire Italian peninsula. By the following century it included North Africa, the Iberian Peninsula, Greece, and what is now southern France. Two centuries after that, towards the end of the 1st century BC, it included the rest of modern France, and much of the east. By this time, despite the Republic's traditional and lawful constraints against any individual's acquisition of permanent political powers, Roman politics was dominated by a small number of Roman leaders, their uneasy alliances punctuated by a series of civil wars.

The final victor in these civil wars, Octavian (later Augustus), reformed the Republic as a Principate, with himself as Rome's "first citizen" (princeps). The Senate continued to sit and debate. Annual magistrates were elected as before, but final decisions on matters of policy, warfare, diplomacy and appointments were privileged to the princeps as "first among equals" (or imperator due to the holding of imperium, from which the term emperor is derived). His powers were monarchic in all but name, and he held them for his lifetime, on behalf of the Senate and people of Rome. The Roman Republic was never restored, but neither was it abolished, so the event that signaled its transition to Roman Empire is a matter of interpretation. Historians have variously proposed the appointment of Julius Caesar as perpetual dictator in 44 BC, the defeat of Mark Antony at the Battle of Actium in 31 BC, and the Roman Senate's grant of extraordinary powers to Octavian (Augustus) under the first settlement in 27 BC, as candidates for the defining pivotal event ending the Republic.

I Claudius for those who've never heard of it

The BBC won awards for their TV version