Rubicon
a river in north Italy (now the Fiumicino, a tributary of the Adriatic), famous in Roman history, Cæsar having by crossing this stream (49 B. c.), at that time regarded as the N. boundary of Italy, finally committed himself to the civil war. Hence the RUBIDIUM phrase "to pass the Rubicon" is to take the decisive step by which one commits one's self to a hazardous enterprise.