Crossing the Rubicon

The phrase "crossing the Rubicon" is an idiom meaning "passing the point of no return".¹ 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,² which eventually led to Caesar becoming dictator for life (dictator perpetuo).

Caesar had previously been appointed governor of a region that stretched from southern Gaul to Illyricum. As his term was coming to an end, the Senate ordered him to disband his army and return to Rome. Caesar defied the order, and instead brought his army to Rome, occupying the city of Ariminum³ then crossing the Rubicon towards the south. The exact date of the crossing is unknown,⁴ but scholars usually place it on the night of 10 and 11 January because of the speeds at which messengers could travel at that time.⁵ The phrase alea iacta est ("the die is cast"), allegedly uttered by Caesar just before the crossing, also comes from this event.

History

During the late Roman Republic, the river Rubicon was a small river that flowed east from the into the . It was one of two rivers that marked the boundary between the of to the north and areas controlled directly by Rome and its to the south; west of the Apennines, the border was marked by the river , a much wider and more important waterway which flows into the .