Julius Caesar's crossing the Rubicon River was an event in 49 BC that precipitated the Roman Civil War, which ultimately led to Caesar becoming dictator for life and the rise of the imperial era of Rome. Caesar had been appointed to a governorship over a region that ranged from southern Gaul to Illyricum (but not Italy). As his term of governorship ended, the Roman Senate ordered Caesar to disband his army and return to Rome. He was explicitly ordered not to bring his army across the Rubicon River, which was at that time a northern boundary of Italy. In January of 49 BC, Caesar brought the 13th legion across the river, which the Roman government considered insurrection, treason, and a declaration of war on the Roman Senate. According to ancient texts, he is said to have uttered the phrase "alea iacta est”, depending on subtle translation differences either “The die is cast” or “The game is afoot”, as his army marched through the shallow river.
Today, the phrase "crossing the Rubicon" is an idiom that means to pass a point of no return.
