Today in History—January 10: An Irreversible Decision

On a starlit night in 49 bce, Julius Caesar and his army crossed the Rubicon River—which was more of a stream, really—to take control of the Roman Republic. The decision to cross the symbolic and literal boundary between Caesar’s territory of Gaul (located in modern-day France) and Italy was not made lightly: It violated the law that forbade generals from leading armies out of their assigned territories. Caesar’s act of defiance marked the beginning of a four-year Roman Civil War and Rome’s transition from republic to empire.

Before beginning his trek, Caesar sent an advance team ahead. The entire operation relied on the element of surprise, as the Italian town of Ariminum (Rimini today, in northern Italy on the Adriatic Sea) had fortifications that could be used in the case of invasion. The route would give him access to many of Italy’s main roads.

According to one Greek historian, before Caesar crossed the Rubicon, he saw a mysterious apparition that blew a war trumpet and beckoned him to cross. It was at this moment that Caesar uttered the Latin phrase “Alea iacta est!” (“The die is cast!”), which is now used to mark a point of no return.

After marching for a few hours, Caesar’s men entered Ariminum; the city’s guards had been neutralized by the advance party. Greek historian Plutarch later described the takeover as Caesar taking “advantage of the golden moment” with “amazing boldness and speed.”

Word of Caesar’s daring maneuver reached Rome five days later, leading to mass panic and exodus. Apparently the gods were displaying some violence at the time as well—the historian Dio Cassius described wolf sightings, a solar eclipse, comets, and a vengeful lightning strike on the capitol following the invasion. Caesar’s Ariminum action eventually made him Rome’s dictator, though he was killed by senators soon after his ascent to power.

The move also ushered a new phrase into the lexicon. More than 2,000 years later, “crossing the Rubicon” means committing to something irrevocably—and accepting the consequences.