The Roman general who famously crossed the Rubicon to start a civil war was Julius Caesar. In January 49 BC, Caesar crossed the Rubicon River with his army, a courageous act that defied the Senate's orders and led to a conflict with his political rival, Pompey. The phrase "crossing the Rubicon" has since become a metaphor for making an irreversible decision. Caesar's actions initiated a series of civil wars that ultimately led to his rise as dictator and the end of the Roman Republic. The ensuing conflict transformed Rome into an empire under his rule and established significant changes in governance.