How did ancient Roman law limit military arms near the Rubicon?

Ancient Roman law did not specifically regulate "gun control" in the modern sense, as firearms did not exist in antiquity. Instead, Roman law focused on the legal boundaries of military command to maintain the stability of the state.

The restriction relevant to the Rubicon was the Lex Cornelia Majestatis, which forbade a general from leading an army out of the province to which he had been assigned by the Senate. In 49 BCE, Julius Caesar violated this law by crossing the Rubicon—a small stream marking the boundary between his province of Gaul and Italy—with his forces.12

This act was considered a declaration of war against the Roman state, as it bypassed the legal authority governing the movement of armed legions into the Italian heartland. Rather than a policy on individual arms, this was a constitutional safeguard designed to prevent military commanders from using their troops to threaten the central government and seize power.12