The Leaning Tower of 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 it is the third structure by time in Pisa's Piazza del Duomo (Cathedral Square).
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 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 tonnes. The tower has 296 steps (the seventh floor has a different number of steps on the two sides, if you climb it on the north part you can count only 294 steps). The tower leans at an angle of 3.97 degrees. This means that the top of the tower is 3.9 meters from where it would stand if the tower were perfectly vertical.
There has been controversy about the real identity of the architect of the Leaning Tower of Pisa. For many years, the design was attributed to Guglielmo and Bonanno Pisano , a well-known 12th-Century resident artist of Pisa, famous for his bronze casting, particularly in the Pisa Duomo. Bonanno Pisano left Pisa in 1185 for Monreale, Sicily, only to come back and die in his home town. His sarcophagus was discovered at the foot of the tower in 1820. However recent studies seems to indicate Diotisalvi as the original architect, by construction affinities with his other works, like the Baptistery in Pisa...(more on www.wikipedia.org)