In 1990, the Leaning Tower of Pisa was closed after its dangerous tilt raised fears of collapse; how engineers used a bizarre trick to move the 14,000-ton tower back 17 inches without making it straight

In 1990, the Leaning Tower of Pisa in Italy was closed for repairs. What was the problem? The tower, built over a period of 200 years, between 1173 and 1372 A.D., was leaning too much. The 1990 closure was the first time in the tower's long life that it was was closed for repair. Today, the tower is back where it belongs but it is leaning about 18 inches less than before.

By 1990, the Leaning Tower of Pisa had tilted more than 5.5 degrees, with the top leaning about 15 feet beyond its base. The pressure on the medieval stonework at the bottom was becoming dangerous, raising fears that the tower could collapse, according to a report in Science Blog.