The Roman Republic was the phase of ancient Roman characterized by a republican form of government; a period which began with the overthrow of the Roman monarchy, c. 509 BC, and lasted over 450 years until it was subverted, through a series of civil wars, into the Principate form of government and the Imperial period.
The Roman Republic was governed by a complex constitution, which centered on the principles of a separation of powers and checks and balances. The evolution of the constitution was heavily influenced by the struggle between the aristocracy, or the patricians, and other talented Romans who were not from famous families, the plebeians. Early in its history, the Republic was controlled by an aristocracy of individuals who could trace their ancestry back to the early history of the kingdom. Over time, the laws that allowed these individuals to dominate the government were repealed, and the result was the emergence of a new aristocracy which depended on the structure of society, rather than the law, to maintain its dominance. Thus, only a revolution could overthrow this new aristocracy.
Rome also saw its territory expand during this period, from central Italy to the entire Mediterranean world. During the first two centuries, Rome expanded to the point of dominating Italy. During the next century, Rome grew to dominate North Africa, Iberia, Greece, and what is now southern France. During the last two centuries of the Roman Republic, Rome grew to dominate the rest of modern France, as well as much of the east. By this point, however, the republican political machinery was replaced with imperialism.