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The exact date of the transition to the Roman Empire 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. Most, however, 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.
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Rome was initially a little kingdom and the king system endured more than 200 years. In 509 aC it fell, the last king was exhiled, and the republican system began.