Where does the phrase 'crossing the rubicon' come from?

The phrase "crossing the Rubicon" originates from Julius Caesar's decision in 49 BC to lead his army across the Rubicon River in northern Italy, an act that was considered treasonous and effectively declared war on the Roman Senate. The phrase symbolizes making a significant and irreversible decision that commits one to a course of action. It has since been used metaphorically to describe situations where individuals or groups take bold, decisive actions with far-reaching consequences.