Pisa is best known for its great structure, the Leaning Tower of Pisa, built between 1173-1350. The tower was built as a statement of Pisa's strength to its rival city, Florence. There are two main theories as to why the tower leans. One theory says the soil around the tower is soft and can't hold the weight of the structure. The other says that the tower was built to lean! Which do you believe? (DENNIS FLAHERTY—GETTY IMAGES)