The Leaning Tower of Pisa is one of the wonders of the medieval world. It is located in the Campo dei Miracoli (field of miracles) in the Italian city of Pisa, and is 55.863 meters in height. It is a freestanding bell tower. It is not clear who designed the tower, because the construction was carried out over an extended period of more than a century.
It was designed to be vertical, but started to lean during its construction. It leans at an angle of 3.97 degrees. It has fine mosaic pavements, elaborately carved columns, and numerous bas-reliefs. It is made of white marble. It is a famous tourist attraction and gives a panoramic view of the city.
In 1172, a wealthy Italian widow named Berta di Bernardo left 60 cents in her will to purchase stones and construct a bell tower. The construction began on August 9, 1173.
The tower began to sink after the construction reached the third floor, in 1178. This was because the tower had a mere three-meter foundation, set in weak, unstable subsoil. Construction of the tower was halted for almost a hundred years, since the city-state of Pisa was engaged in wars with Florence, Genoa and Lucca.
In 1182, the 'Opera Campanilis petrarum Sancte Marie' (Stone Works of bell tower of Saint Mary) was established. In 1185, probably there was an interruption at the height of the fourth order.
Giovanni di Simone restarted the construction in 1272. In 1292, he measured the inclination of the tower with a plumb line. The final two floors of the tower were added between 1319 and 1350. In 1360, Tommaso Pisano completed, erecting the belfry and making the last important geometric correction of the structure. In 1372, the bell chamber was added on top.
In 1993, 650 tons of lead were hanged from the North side of the building, which stopped the leaning from increasing for a while. In 1987, the tower was declared a part of the Piazza dei Miracoli UNESCO World Heritage Site. In 1995, an attempt was made to expand the foundations under the south side of the building.
The ground was frozen using liquid nitrogen, to stop it from moving. Stones were removed from the tower in order to insert metal rods. However, it was not known that the removed stones were part of the original foundation of the building. In one night, the lean increased as much as it normally would over 2 years. 250 tons of lead were quickly added.
A British engineering professor came up with the idea of removing ground soil from under the high side of the tower instead of trying to strengthen the low side by adding to its foundation. Work began in 1999 and was done extremely slowly so that the tower wouldn't get a sudden shock.
When the work was completed, at the beginning of June 2001, the tower had been straightened by about 16 inches, which was its position way back in 1838. In May 2008, after the removal of 70 tons of earth, the tower had stabilized. The engineers estimated that the tower would be stable for at least the next 200 years.
If you want to visit this epic monument, you have got plenty of time to do that, then!