While the tower was supposed to stand upright , after construction began in 1173 , she began to lean towards the south- east due to poor foundation and pledged a loose substrate, it became the basis for the change of direction . Currently, the tower leans to the southwest .
The tower is 55.86 m ( 183.27 m ) from the ground on the lowest side and 56.70 m ( 186.02 m ) on the highest side. The wall thickness at the base of 4.09 m ( 13.42 m ) and at the top 2.48 m (8.14 m). Its weight is estimated at 14 500 tonnes.
The tower has 296 or 294 steps.Before restoration work carried out during the period from 1990 to 2001 , the tower tilted at an angle of 5.5 degrees, but now the tower tilts 3.99 degrees.
The construction of the towers were built in two phases , starting from August 9, 1173, and with two long interruptions, lasted almost 200 years, until 1360 .
Author of the project remained unknown.Without a doubt , the tower is one of the most remarkable bell towers in Europe. Once thought that the slope of the tower was part of the project, but now this version is unlikely.
As for the slope and due to original architecture, from 1173 until the present day , the tower is under scrutiny .Continuing efforts to make the tower more stable. For example, crumbling pillars have been replaced several times. Now mainly carried out underground work, reinforcing the foundation.
Once again, December 15, 2001 Tower opened its doors to tourists.
December 30, 1986 UNESCO awarded World Heritage status architectural ensemble of the (cathedral (Piazza del Duomo), baptistry , bell tower ( the Tower of Pisa ) and the cemetery ).
The architecture of the ensemble had a great influence on monumental art in Italy XII-XIV centuries.
In 2008, scientists have once again stated that a further fall of the Tower closed. Until then , despite numerous efforts to freeze , the tower continued to deviate from the vertical at a speed of 1 mm per year .
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