Julius Caesar's Rubicon Crossing in 49 BC and the Collapse of the Roman Republic

On January 10 or 11, 49 BC, Julius Caesar led his troops across the Rubicon River into Italy, an act that ignited civil war and ultimately transformed the Roman Republic into an empire ruled by Caesars for five centuries. Caesar's aim was not revolution but to avoid prosecution, secure the consulship, and obtain a military command. The Senate had declared him a public enemy on January 7, 49 BC. Earlier, the First Triumvirate—a secret alliance of Caesar, Pompey the Great, and Marcus Licinius Crassus formed in 60 BC—had dominated Roman politics. Caesar's consulship in 59 BC pushed through the lex Julia agraria to settle Pompey's veterans, and later the triumvirate was renewed in 56 BC, granting Caesar a five-year extension in Gaul. Crassus died at the Battle of Carrhae in 53 BC, and Pompey became sole consul in 52 BC. By 49 BC, Pompey had sided with Caesar's opponents. After crossing the Rubicon, Caesar defeated Pompey at the Battle of Pharsalus in 48 BC; Pompey fled to Egypt and was killed. Caesar was assassinated on the Ides of March, 44 BC. His heir Octavian, later Augustus, won the ensuing civil wars by 30 BC and established the principate, creating a precedent for imperial rule that lasted for centuries.