The architect who completed the construction was Tommaso Pisano (1350–1372). The Tower of Pisa's lean enters the tale in 1173, when building begins. It had began to tilt by the time its builders reached the third storey, in 1178, due to the soft ground. They immediately started work on the fourth storey, but it is not known if this prevented further tilting of the tower.
Tommaso was born in Pisa to a family who were stone masons. After his father died when he was young, his mother married another stone mason who took her home to Florence. Tommaso wanted to follow in their footsteps and go to Venice, but his mother did not want him to leave so she sent him to Rome to study under an architect there. When he returned home he got a job offer from Pisa's city council and moved there with his wife and son. He built several other towers in Italy before coming to the Leaning Tower of Pisa where he finished his career. He died in 1372 at the age of 36.
It had begun to tilt by the time its builders reached the third storey, in 1178, due to the soft ground.
The Pisa Leaning Tower is not only one of the most famous landmarks in Piazza dei Miracoli but also the largest tilted building in the world. The tower leans 3.8 degrees to its west side.
It is believed that during construction it must have shifted somewhat from east to west, causing it to lean over time. The cause of this movement has never been determined with certainty but many theories have been put forward. It may have been due to a landslide or an earthquake. Or it could have been as simple as water leaking into a foundation hole causing the structure to tilt.
Whatever the reason, the effect of the leaning tower on visitors today is quite dramatic. By standing under it, you get a feeling for how high up you are above street level. You can also see how the tower has affected other buildings around it: some add their own slight inclines to create a unique experience for those who visit them.
There are actually several different ways to describe this phenomenon. Geologists call it "scalenoning" because it creates a picture of someone's skull when viewed from the right angle.
The tower began to tilt dramatically soon after construction began in 1173. Engineer Bonnano Pisano, who planned the tower, attempted to remedy issue by simply curling it higher as construction progressed. On the north side, they raised the pillars on the third and eighth levels. "It's like a banana," adds Burland. "If you pull on its ends, it'll straighten out." But despite these efforts, the tower continued to lean.
In 1256, another engineer, Nicola Pacenti, came up with a more permanent solution. He built an arcade of arches beneath the level where the leaning tower now stands. The arches connect to a large chamber that contains the tower's foundation. This action should have fixed the problem; but within a few years, the arcade started to collapse due to lack of maintenance. By 1330, only four of the original twenty-two arches remained.
In 1464, yet another engineer, Antonio di Duccio, repaired the arcade by building an additional set of arches above the damaged section. These new arches were made of wood and covered in copper when they were first constructed, but over time they too have collapsed. Only three of the original fourteen arches from this repair remain today.
The tower continues to deteriorate. In 1564, Giovanni della Robbia created a sculpture for the base of the tower which represents Moses parting the Red Sea.
The true identity of the architect of the Leaning Tower of Pisa has been a source of contention. For many years, the design was credited to Guglielmo and Bonanno Pisano, a well-known 12th-century Pisan resident artist famed for his bronze casting, notably in the Pisa Duomo. However, recent research has shown that neither brother was involved in the project. Instead, they probably hired an outside architect to create their plan.
The first certain evidence we have of someone calling himself an "architect" is Ammannato di Giovanni di Bonino del Carbone, who signed a contract with the Pisans on August 18, 1163. This makes him at least 21 years old, since Giovanni di Bonino was born in 1127. So he had to have begun his career before 1151, the year in which he signed the contract as an "architect."
Ammannato was not a native Italian but a foreigner who had settled in Italy. He came from Bologna and was most likely born around 1135. The only other thing we know about him is that he died in 1180/81, which means he built nothing else after signing the contract with the Pisans in 1163. This fact alone would not normally be enough to disqualify him as the creator of the Leaning Tower, but he has another problem to answer for: he was canonized by the Catholic Church in 1199.
The tower was stabilized as a result of restoration work completed between 1999 and 2001. Engineers placed weights on the structure's north end while removing earth from below, forcing it to sink back in that direction gradually. The Leaning Tower of Pisa still leans south, although at just 3.99 degrees. It is assumed that this amount of leaning will not cause any problems.
In response to questions from tourists about its stability, the tower's owner, the University of Pisa, posts bulletins on its website warning that the tower is not stable and urging visitors not to climb it.
In addition to the weight placed on the north end, parts of the base are also weighted to counterbalance the effect of soil being removed near the foundation.
Engineers use the same technique to stabilize other tilted buildings, such as the Capitol Building in Washington, D.C., and the Uffizi Gallery in Florence, Italy. In both cases, they have been able to reduce the tilt to within safety limits by creating vertical ridges at the bases of the structures using heavy equipment.
The practice has also been used with success in combating erosion near riverbanks. When soil is removed from areas around the base of the tower, it causes the tower to lean further into the empty space. As a result, water flows off the top of the tower and not into these holes, preventing further erosion.