On this day in history, January 10, Gaius Julius Caesar crossed the Rubicon River and began Civil War in Rome.
The Roman civil war of 49 BC, sometimes called Caesar's Civil War, is one of the last conflicts within the Roman Republic. It was a series of political and military confrontations between Julius Caesar, his political supporters, and his legions, against the traditionalist conservative faction in the Roman Senate, sometimes known as the Optimates, backed by legions loyal to Pompey.
After a long political and military struggle, between 49 and 45 BC, which would take in battles in Italia, Greece, Egypt, Africa, and Hispania, Caesar finally defeated the last of the traditional faction of the Roman senate at the Battle of Munda and became dictator.
Caesar's civil war and its resulting changes in Roman government all but swept away the political traditions of the Roman Republic, a blow which eventually lead to the Roman Empire. On January 10, 49 BC Caesar crossed the Rubicon with one legion, the Legio XIII Gemina. The Rubicon marked the boundary between the Roman province of Cisalpine Gaul to the north and Italy proper to the south, and Roman law forbade any general from crossing it with an army. The purpose of the law was to protect the republic from internal military threat. Caesar's action thus marked the beginning of the civil war.
Historians differ as to what Caesar said upon crossing the Rubicon; the two major competing lines are "Alea iacta est" ("The die is cast"), and "Let the dice fly high!" (a quotation from a line by the New Comedy poet Menander). This minor controversy is occasionally seen in modern literature when an author attributes the less popular Menander line to Caesar.