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     In 49 BCE, with the dramatic proclamation "the die is cast," Julius Caesar made the fateful decision to cross the Rubicon River at the head of his 13th Legion.  The crossing of the Rubicon was momentous because the river demarcated the boundary between Italy and the province of Gaul to the north, where Caesar was serving as governor.  Suspicious of his growing power, the Senate had ordered him to disband his army and return to Rome.  But Caesar, defying the Senate, decided to return not in submission but in rebellion, marching on Rome with his legion.  By crossing into Italian territory with an army, Caesar had irrevocably made himself a traitor.
     For all its notoriety, Caesar's river crossing was a relatively modest affair in which the future ruler and his legionnaires merely waded across a shin-deep stream.  Nonetheless, this act put him in irreconcilable opposition to Rome's Senate, making the expression "crossing the Rubicon" forever synonymous with passing a point of no return.

-General Stanley McChrystal,  Leaders:  Myth and Reality