An ancient Latin name for a small river in northern Italy which flows into the Adriatic Sea. It marked the boundary between the Roman province of Gaul and the Roman heartland. Its crossing by Julius Caesar in 49 BC began a civil war
{i} river in northern Italy (the act of crossing this river is seen as a momentous act)
If you say that someone has crossed the Rubicon, you mean that they have reached a point where they cannot change a decision or course of action. He's crossed the Rubicon with regard to the use of military force as an option. cross the Rubicon to do something that will have extremely important effects in the future and that you cannot change (Rubico river in northern Italy which Julius Caesar crossed in 49BC, setting off a civil war). Small stream that separated Cisalpine Gaul from Italy in the era of the Roman republic. The movement of Julius Caesar's forces over the Rubicon into Italy in 49 BC violated the law that forbade a general to lead an army out of the province to which he was assigned. Caesar's act thus amounted to a declaration of war against the Roman Senate and resulted in the three-year civil war that left Caesar ruler of the Roman world. "Crossing the Rubicon" became a popular phrase describing a step that irrevocably commits a person to a given course of action