The Roman Republic was the period of the ancient Roman civilization where the government operated as a republic. It began with the overthrow of the Roman monarchy, traditionally dated around 509 BC, and its replacement by a government headed by two consuls, elected annually by the citizens and advised by a senate. A complex constitution gradually developed, centered on the principles of a separation of powers and checks and balances. Except in times of dire national emergency, public offices were limited to one year, so in theory at least, no single individual could dominate his fellow citizens.
In practice, Roman society was hierarchical. 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 Over time, the laws that gave Patricians exclusive rights to Rome's highest offices were repealed or weakened, and a new aristocracy emerged from among the plebeian class.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.
Many of Rome's legal and legislative structures can still be observed throughout Europe and the rest of the world by modern nation state and international organizations. The Romans' Latin language has influenced grammar and vocabulary across parts of Europe and the world.
Constitution
The Constitution of the Roman Republic was a set of guidelines and principles passed down mainly through precedent.The constitution was largely unwritten, uncodified, and constantly evolving. Rather than creating a government that was primarily a democracy (as was ancient Athens), an aristocracy (as was ancient Sparta), or a monarchy (as was Rome before and, in many respects, after the Republic), the Roman constitution mixed these three elements, thus creating three separate branches of government. The democratic element took the form of the legislative assemblies, the aristocratic element took the form of the Senate, and the monarchical element took the form of the many term-limited consuls.
The ultimate source of sovereignty in this ancient republic, as in modern republics, was the demos (people). The People of Rome gathered into legislative assemblies to pass laws and to elect executive magistrates. Election to a magisterial office resulted in automatic membership in the Senate (for life, unless impeached). The Senate managed the day-to-day affairs in Rome, while senators presided over the courts. Executive magistrates enforced the law, and presided over the Senate and the legislative assemblies.