Rubicon

ru'bi-kon, in classical geography, a little stream in Italy, dividing the province of Gaul from Rome proper. When the Senate at Pompey's instigation gave orders to send home part of his army, Caesar, it is said, rode up and down the banks of the Rubicon debating with himself all night whether to comply or to march on Rome. At daybreak he gave marching orders; hence the proverbial expression, "crossing the Rubicon," denotes taking a decisive step which cannot be retraced. See Caesar; Pompey