"Rubicon" (Rubicō, Italian: Rubicone) is a 29km long river in northern Italy. The river flows from the Appennines to the Adriatic sea through the southern Emilia-Romagna region between the towns of Rimini and Cesena. Since the river has changed its riverbed many times through the years, it is not possible to affirm where the original Rubicon flowed when Julius Caesar crossed it. However, it is common to identify those historical waters to be the current Pisciatello river, since the current Rubicon abandoned its original riverbed.
"Crossing the Rubicon" is a popular idiom meaning to go past a point of no return; the river was a Roman boundary between Cisalpine Gaul and Italy. Julius Caesar crossed the river in 49 BC deliberately as an act of war. On this occasion, Suetonius quoted Caesar as saying, "the die is cast".