How Julius Caesar Started a Big War by Crossing a Small Stream
In 49 B.C. on the banks of the Rubicon, Julius Caesar faced a critical choice. To remain in Gaul meant forfeiting his power to his enemies in Rome. Crossing the river into Italy would be a declaration of war. Caesar chose war.
By Fernando Lillo Redonet
On January 10, 49 B.C., on the banks of the Rubicon River in southern Gaul (near the modern-day city of Ravenna), Julius Caesar and the soldiers of the 13th Legion waited and weighed their options.
The Rubicon is, in reality, little more than a stream. Its significance to Rome lay in its location, marking the official border between Italy and Cisalpine Gaul, the region south of the Alps governed by Julius Caesar. Despite its appearance, crossing this humble river would have serious consequences. According to the law of the Roman Republic, any provincial governor leading troops across the border back into Italy would be declared a public enemy. It was, quite simply, an act of war.
https://www.nationalgeographic.com/archaeology-and-history/magazine/2017/03-04/julius-caesar-crossing-rubicon-rome/
