Julius Caesar swam the Rubicon in 49 BC.
Julius Caesar . Caesar refused the order , and instead marked his defiance in 49 BC by crossing the Rubicon with the 13th Legion , leaving his province and illegally entering Roman Italy under arms . The Rubicon ( Latin : Rŭ́bĭcō , Italian : Rubicone ) is both the name of a shallow river in northeastern Italy , just south of Ravenna , and the name historically given to a river that was famously crossed by Julius Caesar in 49 BC .