What river did Caesar famously cross to precipitate the Roman Civil War?
In 49 BCE, Caesar led his army across the Rubicon River, which separated Gaul from the Italian peninsula. Leading an army into Rome was forbidden by law, and in doing so, Caesar declared himself an enemy of the Roman Senate when he entered its territory. The act sparked a five-year civil war, and when Caesar emerged the victor, he was declared dictator for life.
Source: ThoughtCo