Turin is located in northwest Italy. It is surrounded on the western and northern front by the Alps and on the eastern front by a high hill that is the natural prosecution of the hills of Monferrato. Four major rivers pass through the city: the Po and two of its tributaries, the Dora Riparia (later changed to "Duria Minor" by the Romans, from the Celtic duria meaning "water"), the Stura di Lanzo, and the Sangone.