The Roman general who crossed the Rubicon River, igniting a civil war, was Julius Caesar. In January 49 BCE, he made the fateful decision to lead his army across the Rubicon, effectively declaring war against the Roman Senate and Pompey the Great, his political rival. This act was a direct challenge to the authority of the Senate and marked the beginning of a series of civil wars that would ultimately lead to Caesar becoming dictator for life. The phrase "crossing the Rubicon" has since become synonymous with committing to a significant and irreversible action.