Leaning Tower of Pisa, Italian Torre Pendente di Pisa, medieval structure in Pisa, Italy, that is famous for the settling of its foundations, which caused it to lean 5.5 degrees (about 15 feet [4.5 metres]) from the perpendicular in the late 20th century. Extensive work was subsequently done to straighten the tower, and its lean was ultimately reduced to less than 4.0 degrees.