What Does It Mean to Cross the Rubicon?

Julius Caesar leading his army across the Rubicon
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To cross the Rubicon means to take an irrevocable step that commits one to a specific course. When Julius Caesar was about to cross the tiny Rubicon River, he quoted from a play by Menander to say "let the die be cast." But what kind of die was Caesar casting and what decision was he making?

Before the Roman Empire

Before Rome was an Empire, it was a Republic. Julius Caesar was a general of an army of the Republic, based in the north of what is now Northern Italy. He expanded the borders of the Republic into modern France, Spain, and Britain, making him a popular leader. His popularity, however, led to tensions with other powerful Roman leaders.

Having successfully led his troops in the north, Julius Caesar became governor of Gaul, part of modern-day France. But his ambitions were not satisfied. He wanted to enter Rome itself at the head of an army. Such as act was forbidden by law.

At the Rubicon

When Julius Caesar led his troops from Gaul in January of 49 B.C.E., he paused on the northern end of a bridge. As he stood, he debated whether to cross or not the Rubicon, a river separating Cisalpine Gaul from Italy. When he was making this decision, Caesar was contemplating committing a heinous crime.

If he brought his troops into Italy, he'd be violating his role as a provincial authority and would essentially be declaring himself an enemy of the state and the Senate, fomenting civil war. But if he didn't bring his troops into Italy, Caesar would be forced to relinquish his command and probably go into exile, giving up his military glory and political future.

Caesar definitely debated for a while about what to do. He realized how important his decision was, especially since Rome had already undergone ​civil dispute a few decades earlier. According to Suetonius, Caesar quipped, "Even yet we may draw back, but once cross yon little bridge, and the whole issue is with the sword." Plutarch reports that he spent time with his friends "estimating the great evils of all mankind which would follow their passage of the river and the wide fame of it which they would leave to posterity." 

The Die Is Cast

A die is simply one of a pair of dice. Even in Roman times, gambling games with dice were popular. Just as it is today, once you've cast (or thrown) the dice, your fate is decided. Even before the dice land, your future has been foretold.

When Julius Caesar crossed the Rubicon, he started a five-year Roman civil war. At the war's end, Julius Caesar was declared dictator for life. As dictator, Caesar presided over the end of the of the Roman Republic and the start of the Roman Empire. Upon Julius Caesar's death his adopted son, Augustus became Rome's first emperor. The Roman Empire started in 31 B.C.E. and lasted until 476 C.E.