The Leaning Tower of Pisa is located in Pisa, Italy. The tower was built in the 12th century and before it became famous for its lean, it was intended to be a bell tower. As the lean became more pronounced over the years, the tower was closed off to the public in 1990 in an effort to try to stabilize it. Considered a success, the project took just over 10 years to complete, and the much safer tower has since reopened to the public.
With the lean of the tower reaching a critical point, in terms of safety, the Leaning Tower of Pisa was studied by numerous engineering groups and mathematicians, all looking to find a solution to keep the tower from ultimately collapsing. The bells were removed and cables put around the third level to keep the tower from falling. However, these were only marginally effective and the tower continued its slow, but steady lean towards the ground.
The most successful attempt to straighten the tower back to its original lean degree and stabilize it occurred in the late 1990s, and involved the careful removal of dirt from the high side of the tower. This eventually moved the tower nearly 18 inches back towards center, putting the tower back to its 1838 lean position. It was effective enough that the engineers working on the project declared the tower stable for at least another 300 years. It was the first time in the tower's history that it had stopped moving.