Rubicon

Rubicon River
The mouth of the Rubicon in Cesenatico
Country	Italy
Basin features
Main source	Sogliano al Rubicone 250 m (820 ft)
River mouth	Adriatic Sea
Physical characteristics
Length	80 km (50 mi)

The Rubicon (Latin: Rŭ́bĭcō, Italian: Rubicone) is both the name of a shallow river in northeastern Italy, just south of Ravenna, and the name historically given to a river that was famously crossed by Julius Caesar in 49 BC. While it has not been proven, historians generally agree that the two rivers are indeed one and the same; this was not always the case.

The modern-day river runs around 80 kilometers, from the Apennine Mountains to the Adriatic Sea through the southern Emilia-Romagna region, between the towns of Rimini and Cesena. The Latin word rubico comes from the adjective rubeus, meaning "red". The river was so named because its waters are colored red by mud deposits.

During the Roman republic, the river Rubicon marked the boundary between the Roman province of Cisalpine Gaul to the north-east and Italy proper (controlled directly by Rome and its socii (allies)) to the south. On the north-western side, the border was marked by the river Arno, a much wider and more important waterway, which flows westward from the Apennine Mountains (it and the Rubicon rise not far from each other) into the Tyrrhenian Sea.

Governors of Roman provinces were appointed promagistrates with imperium (roughly, "right to command") in their province(s). The governor would then serve as the general of the Roman army within the territory of his province(s). Roman law specified that only the elected magistrates (consuls and praetors) could hold imperium within Italy. Any promagistrate who entered Italy at the head of his troops forfeited his imperium and was therefore no longer legally allowed to command troops.