"I've crossed the Rubicon"

The river is notable as Roman law forbade any general from crossing the Rubicon with a legion. The river was considered to mark the boundary between the Roman province of Cisalpine Gaul to the north and Italy proper to the south; the law thus protected the republic from internal military threat. A Roman general was thus obliged to disband his army before crossing the Rubicon, otherwise both he and his men were guilty of high treason and sacrilege, and automatically condemned to death.

When Julius Caesar crossed the Rubicon with his army in 49 BC, supposedly on January 10 of the Roman calendar, to make his way to Rome, he broke that law and made armed conflict inevitable. According to historian Suetonius, Caesar uttered the famous phrase ālea iacta est ("the die has been cast"). Caesar's decision for swift action forced Pompey, the lawful consul, and a large part of the Senate to flee Rome in fear. Since Caesar was eventually victorious, the punishment due him became a moot issue.

(via wikipedia)

:-)