Why is the Tower of Pisa leaning?

 

 

 

 

 

Leaning Tower of Pisa

The Leaning Tower of Pisa is the bell tower, of the cathedral of the Italian city of Pisa, known worldwide for its unintended tilt to one side. The tower's tilt began during construction, caused by an inadequate foundation on ground too soft on one side to properly support the structure's weight.
 

Construction of the tower occurred in three stages across 344 years. Work on the ground floor of the white marble campanile began on August 14, 1173, during a period of military success and prosperity. The tower began to sink after construction had progressed to the second floor in 1178. This was due to a mere three-metre foundation, set in weak, unstable subsoil . The total amount of years that the building of the tower took was between 185 and 195 years.
 

The tilt increased in the decades before the structure was completed, and gradually increased until the structure was stabilized (and the tilt partially corrected) by efforts in the late 20th and early 21st centuries.
 

The height of the tower is 55.86 m from the ground on the low side and 56.70 m on the high side. The tower has 296 or 294 steps; the seventh floor has two fewer steps on the north-facing staircase. Prior to restoration work performed between 1990 and 2001, the tower leaned at an angle of 5.5 degrees, but the tower now leans at about 3.99 degrees. This means that the top of the tower is displaced horizontally 3.9 metres from where it would be if the structure were perfectly vertical.