The famous military general who crossed the Rubicon River in 49 BCE was Julius Caesar. By crossing the Rubicon, Caesar defied the Roman Senate's orders and ignited a civil war in Rome. This act is famously associated with the phrase "The die is cast," indicating that there was no turning back for Caesar after this bold decision. His crossing of the Rubicon symbolized a point of no return, leading to his eventual rise as dictator and the end of the Roman Republic. This pivotal moment profoundly changed the trajectory of Roman history.