Alea iacta est (Latin: "The die has been cast." Alternate: "The die is cast.") is a Latin phrase attributed by Suetonius (as iacta alea est) to Julius Caesar on January 10, 49 BC, as Caesar led his army across the River Rubicon in Northern Italy. Read here.
The phrase, "the die has been cast," is used to mean events have passed a point of no return; that something inevitable will happen (from the Wikipedia entry sourced above). Historians point to Caesar's Rubicon crossing as the event that ultimately launched the Roman empire, even though the empire actually replaced the republic twenty years after his murder.
The dye has been cast.