Julius Caesar, the notable military leader of ancient Rome, crossed the Rubicon River in 49 BC, an act that would lead to a civil war in Rome. His decision to march his army into Italy was a bold move, as it defied the Roman Senate's authority and represented a point of no return. The phrase "crossing the Rubicon" has since become a metaphor for making an irreversible decision. Caesar’s crossing marked the beginning of his ascent to power and the end of the Roman Republic as he subsequently became dictator. This pivotal moment shaped the future of Roman governance and history, leading to the establishment of the Roman Empire.