Ancient Rome began as villages along the Tiber River that united to form the city of Rome around 750 BC. For over 200 years, Rome was ruled by kings but became a republic in 509 BC with democratic rule divided into legislative, judicial, and executive branches. Under ambitious generals, Rome's armies expanded the republic's territories around the Mediterranean Sea. The successful general Julius Caesar took control of Rome, becoming dictator and ending the republic. After Caesar's assassination, his adopted son Octavian became Rome's first emperor, establishing the Roman Empire. At its height under Emperor Augustus, the Empire encompassed much of Europe and the Mediterranean region. The Empire eventually declined due to overexpansion, economic troubles, and invasions, with