(dark blue), believed to be the same river crossed by Caesar During the late
Roman Republic, the river Rubicon was a small river that flowed east from the
Apennine Mountains into the
Adriatic Sea. It was one of two rivers that marked the boundary between the
Roman province of
Cisalpine Gaul to the north and areas controlled directly by Rome and its
allies to the south; west of the Apennines, the border was marked by the river
Arno, a much wider and more important waterway which flows into the
Tyrrhenian Sea. Governors of Roman provinces were appointed
promagistrates with
imperium (roughly, "right to command") in one or more provinces. The governors then served as generals of the
Roman army within the territory they ruled.
Roman law specified that only the elected
magistrates (
consuls and
praetors) could hold
imperium within Italy. Any magistrate who entered Italy at the head of his troops forfeited his
imperium and was therefore no longer legally allowed to command troops. Exercising
imperium when forbidden by the law was a capital offense. Furthermore, obeying the commands of a general who did not legally possess
imperium was a capital offense. If a general entered Italy in command of an army, both the general and his soldiers became outlaws and were automatically condemned to death. Generals were thus obliged to disband their armies before entering Italy. ==Julius Caesar==