The Leaning Tower of Pisa (Torre pendente di Pisa) is a bell tower in Pisa, Italy.
The Tower of Pisa is world famous for its prominent tilt to one side.
The tower's foundations were built on soft subsoil which had difficulty supporting the tower's weight (14,500 ton). When the second storey was started the lean became noticeable and only got worse as construction continued.
Originally the tower leaned at an angle of 5.5 degrees. After restoration work between 1990 and 2001 this angle was reduced to 3.97 degrees.
The tower is 8 stories high, 55.86 m (183.27 ft) on the low side and 56.67 m (185.93 ft) on the high side.
Construction of the Tower of Pisa started in the year 1173 and was completed in 1372. Construction stopped and restarted twice over those 199 years due to wars.
War stopped construction the first time for almost a century which gave the underlying soil time to settle and compact. If construction had not halted, the tower would most likely have toppled.
As well as the tower, Pisa's Cathedral Square (Piazza del Duomo or Piazza dei Miracoli) also has a cathedral, a baptistery and a cemetery.
The entire Cathedral Square was declared a UNESCO World Heritage Site in 1987.
There are 294 steps on the north side of the tower and 296 steps on the south side.
Seven bells sit in the bell-chamber at the top of the tower, one bell for each note of the musical major scale.
The tower's design has widely been attributed to Guglielmo and Bonanno Pisano however recent studies suggest the architect Diotisalvi may have been involved in the design.
While the original architect of the tower has never been verified many are known to have worked on it including: Bonanno Pisano and Gerardo di Gerardo in phase 1, Giovanni Pisano and Giovanni di Simone during phase 2 before Tommaso di Andrea Pisano oversaw its completion.
Because of the marshy underlying subsoil there are several other towers in Pisa with less prominent tilting issues.
Germans used the tower as a lookout during World War II. The Allies new this but decided against bombing the area due to the impressive beauty of the tower and cathedral.
To demonstrate that speed of descent is independent of an object's mass Galileo Galilei is said to have dropped two cannonballs of differing mass from the tower. However, this is believed to be an old wives' tale.