What does “crossing the Rubicon” mean?

Why a small river mattered

By 50 BC Julius Caesar had spent eight years conquering Gaul, roughly today’s France and Belgium, and his soldiers were loyal to him personally. His command was ending. As a governor he was immune from prosecution; as a private citizen he could be put on trial for things he had done as consul. He offered deals. The Senate refused and ordered him to give up his army.

The border of his province ran along the Rubicon, a small river on the Adriatic coast near Ariminum, today’s Rimini. Roman law kept a governor’s army inside his province. Leading soldiers across that line into Italy made you an enemy of the state.

January 49 BC

Caesar stood on the bank with a single legion. The Roman biographer Suetonius describes him hesitating, then pressing on.

Take we the course which the signs of the gods and the false dealing of our foes point out. The die is cast.

In Latin the famous words are alea iacta est, “the die is cast,” the moment in a game of dice when the throw has left your hand. Plutarch says Caesar actually spoke in Greek, quoting the comic poet Menander: “let the die be cast.” Either way, the crossing gave us two phrases. To cross the Rubicon is to commit to a course with no way back. And “the die is cast” means the decision is made.

What happened next

The crossing worked. Pompey, who once boasted he could raise armies by stamping his foot, abandoned Rome and sailed for Greece. Caesar took Italy in sixty days, raced to Spain to defeat Pompey’s legions there, then crossed to Greece. In August 48 BC he won at Pharsalus against a much larger army. Pompey fled to Egypt and was murdered as he stepped ashore.

Four years later Caesar was dictator for life, and on the Ides of March, 44 BC, senators stabbed him to death. The Republic he had defied did not survive him. His heir became Augustus, Rome’s first emperor.

Which river was the Rubicon?

Nobody is completely sure. The river’s course has shifted since Roman times, and several streams near Rimini were candidates. In 1933 Italy officially renamed one of them, the Fiumicino, as the Rubicone, and the town of Savignano on its banks became Savignano sul Rubicone. Italians still argue about it, which is fitting for a river that is famous only for being crossed.