Construction of the structure now known as the Leaning Tower of Pisa began in 1173, and by the time builders completed the second story, the tower had begun to tilt, due to the soft and sandy soil beneath it. Delayed by various problems, it took nearly 200 years for the Tuscan tower to be completed. And by the late 20th century, the tower was leaning by 5.5 degrees, or nearly 15 feet (4.6 m) off the perpendicular. By the 1990s, Italian engineers feared that the tower might topple “at any moment.” The building was closed for eight years, as engineers hung tons of lead counterweights at the tower’s base, and painstakingly removed soil from around the non-sinking south side. The tower was straightened by 17.7 inches (45 cm) by the end of the conservation efforts in 2001, and in 2008, it was declared that the tower was stable and has stopped moving. Unexpectedly, the tower has self-corrected an additional 1.5 inches (4 cm) closer to perpendicular since 2001.
The Tower of Pisa loses some lean:
- Engineers dug out 20 liters of soil at a time from around the base and installed a system of tunnels and wells to drain the water that was keeping the soil wet and causing the base to sink.
- While digging, remnants of a concrete foundation poured in 1828 were discovered. The engineers created a stronger footing for the tower by strapping it to the foundation with large chains.
- The tower, which attracts thousands of tourists every day, now has the same tilt that it had at the beginning of the 19th century. At some point, though, the tower will stop correcting its list, but it is expected to remain stable for another two centuries.