Cross the Rubicon

The phrase "crossing the Rubicon" is an idiom meaning "passing the point of no return". Its meaning comes from the crossing of the Rubicon river by Julius Caesar in January 49 BC at the head of the 13th Legion. Caesar was not allowed to command an army within Italy proper, and by crossing the river with his forces was defying law and risking death. The crossing precipitated a civil war, which eventually led to Caesar becoming dictator for life.