Passer le Rubicon

Literally: To pass the Rubicon

Example: “En démissionnant publiquement, le ministre a passé le Rubicon.” — By resigning publicly, the minister crossed the Rubicon.

English equivalent: To cross the Rubicon

Origin: Around 49 BC, Julius Caesar was returning from Gaul to a Rome governed by Pompey, who had ordered that any general disband his army before entering Italy. The Rubicon was the river separating Cisalpine Gaul, which Caesar governed, from the Roman republic proper, and it was there he was supposed to lay down his arms. He had no intention of it — he meant to take power. Suetonius has him crossing with his troops on the words alea jacta est, the die is cast, and marching on Rome while Pompey fled. The decision was irreversible and risked civil war; Caesar took it entirely knowingly, and it worked, since he held power after beating Pompey at Pharsalus.