Leaning Tower of Pisa

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.

Engineers sought solutions to the leaning problem, but the tower was ultimately topped out in the 14th century. Twin spiral staircases lined the tower’s interior, with 294 steps leading from the ground to the bell chamber (one staircase incorporates two additional steps to compensate for the tower’s lean). Over the next four centuries the tower’s seven bells were installed; the largest weighed more than 3,600 kg (nearly 8,000 pounds). By the early 20th century, however, the heavier bells were silenced, as it was believed that their movement could potentially worsen the tower’s lean. The foundations have been strengthened by the injection of cement grout and various types of bracing and reinforcement, but in the late 20th century the structure was still subsiding, at the rate of 0.05 inch (1.2 mm) per year, and was in danger of collapse. In 1990 the tower was closed and all the bells silenced as engineers undertook a major straightening project. Earth was siphoned from underneath the foundations, decreasing the lean by 17 inches (44 cm) to 13.5 feet (4.1 metres).

Nation: Italy

Details: https://www.britannica.com/topic/Leaning-Tower-of-Pisa