Pisa's bell tower was begun on August 9, 1173, and it began to sink before it was finished. By 1178, with the second floor built, it was settling into weak, unstable soil on a foundation only about 10 feet (3 m) deep. Work stopped for most of a century during Pisa's wars with its neighbors, which let the ground settle. The bell chamber was added in 1372, 199 years after the start.
The tower is Romanesque, with a ground floor of blind arches and Corinthian capitals, and eight stories of white marble. It stands about 183 feet (55.9 m) tall on its low side, with nearly 300 steps and seven bells. Its architect is uncertain. A 2001 study suggests Diotisalvi, not the long-credited Bonanno Pisano.
By 1990 the lean had reached 5.5 degrees. From 1993 to 2001 engineers added lead counterweights and removed soil from beneath the high side, reducing the tilt to 3.97 degrees. It reopened in December 2001.
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