The Leaning Tower of Pisa (Italian: Torre pendente di Pisa ) or simply The Tower of Pisa ( La Torre di Pisa ) is the campanile, or freestanding bell tower, of the cathedral of the Italian city of Pisa. It is situated behind the cathedral and is the third oldest structure in Pisa's Piazza del Duomo ( Cathedral Square ) after the cathedral and the baptistry. Although intended to stand vertically, the tower began leaning to the southeast soon after the onset of construction in 1173 due to a poorly laid foundation and loose substrate that has allowed the foundation to shift direction. The tower presently leans to the southwest. The height of the tower is 55.86 m (183.27 ft) from the ground on the lowest side and 56.70 m (186.02 ft) on the highest side. The width of the walls at the base is 4.09 m (13.42 ft) and at the top 2.48 m (8.14 ft). Its weight is estimated at 14,500 metric tons (16,000 short tons). The tower has 296 or 294 steps; the seventh floor has two fewer steps on the north-facing staircase. The tower leans at an angle of 3.97 degrees.This means that the top of the tower is 3.9 metres (12 ft 10 in) from where it would stand if the tower were perfectly vertical
The Tower of Pisa was a work of art, performed in three stages over a period of about 177 years. Construction of the first floor of the white marble campanile began on August 9, 1173, a period of military success and prosperity. This first floor is surrounded by pillars with classical capitals, leaning against blind arches. The tower began to sink after construction progressed to the third floor in 1178. This was due to a mere three-meter foundation, set in , unstable subsoil. This means the design was flawed from the beginning. Construction was subsequently halted for almost a century, because the Pisans were almost continually engaged in battles with Genoa, Lucca and Florence. This allowed time for the underlying soil to settle. Otherwise, the tower would almost certainly have toppled. In 1198, clocks were installed on the third floor of the unfinished construction
In 1272, construction resumed under , architect of the Camposanto. In an effort to compensate for the tilt, the engineers built higher floors with one side taller than the other. This made the tower begin to lean in the other direction. Because of this, the tower is actually curved.Construction was halted again in 1284, when the Pisans were defeated by the Genoans in the Battle of Meloria. The seventh floor was completed in 1319. The bell-chamber was not finally added until 1372. It was built by , who succeeded in harmonizing the Gothic elements of the bell-chamber with the Romanesque style of the tower. There are seven bells, one for each note of the musical scale. The largest one was installed in 1655. After a phase (1990-2001) of structural strengthening ,the tower is currently undergoing gradual surface restoration, in order to repair visual damage, mostly corrosion and blackening. These are particularly strong due to the tower's age and to its particular conditions with respect to wind and rain.