Which river was caesar warned not to cross by the roman senate?

Julius Caesar was warned by the Roman Senate not to cross the Rubicon River. In 49 BC, this act was seen as a declaration of war against the Senate and the Republic, as it violated the law prohibiting a general from bringing his army into Italy. Caesar famously defied this warning, leading to a civil war that ultimately resulted in his rise to power. His crossing of the Rubicon has since become a metaphor for making irreversible decisions.