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The Roman Republic (Latin: Res publica Romana; Classical Latin: [ˈreːs ˈpuːb.lɪ.ka roːˈmaː.na]) was the period of ancient Roman civilization beginning with the overthrow of the Roman Kingdom, traditionally dated to 509 BC, and ending in 27 BC with the establishment of the Roman Empire. It was during this period that Rome's control expanded from the city's immediate surroundings to hegemony over the entire Mediterranean world. During the first two centuries of its existence, the Roman 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, Spain, 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, Greece, and much of the eastern Mediterranean. By this time, internal tensions led to a series of civil wars, culminating with the assassination of Julius Caesar, which led to the transition from republic to empire. The exact date of transition can be a matter of interpretation. Historians have variously proposed Julius Caesar's crossing of the Rubicon River in 49 BC, Caesar's appointment as dictator for life in 44 BC, and the defeat of Mark Antony and Cleopatra at the Battle of Actium in 31 BC. However, most use the same date as did the ancient Romans themselves, the Roman Senate's grant of extraordinary powers to Octavian and his adopting the title Augustus in 27 BC, as the defining event ending the Republic.

What marked the beginning of the Roman Republic?
the overthrow of the Roman Kingdom