Julius Ceasar served as governor over the region of Southern Gaul to Illyricum. After he completed his reign as governor, he was instructed by the Senate in Rome to return to Rome, leaving his army behind.
Julius Ceasar did just the opposite because after he completed his tenure, he went along with his soldiers to cross the Rubicon river which was at the boundary of Italy. This act was considered treasonable by the Senate in Rome. It was also considered a declaration of war. Julius Ceasar eventually won the Civil war which protected him from punishment.
in 49BCE, Julius Caesar brought his army to the border of Cilspine Gau and Italy, this was at the Rubicon river. He was thrown between two choice of ignoring the Senate wishes or to take his army into the Italy to confront his Patrician opposition. He chose the later and therefore ignoring his senate wishes.
