Mount Soratte and Tiber Valley, Rome: Monte Soratte is a soaring limestone ridge north of Rome dominating the Tiber River valley. It's 5.5 kilometers long with six main peaks, reaching 691 meters at its high point. The Tiber is the third-longest river in Italy, rising on Monte Fumaiolo in the Apennines and flowing southeast to reach the sea at Ostia. Rome was founded on its banks.