Rubicon (rōˈbĭkŏn) [key], Lat. Rubico, small stream that flows into the Adriatic and in Roman times marked the boundary between Cisalpine Gaul and ancient Italy. In 49 B.C., after some hesitation, Julius Caesar crossed the Rubicon to march against Pompey in defiance of the senate's orders. He thus committed himself to conquer or to perish, and "to cross the Rubicon" now means to take an irrevocable step.
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