Why Does the Leaning Tower of Pisa Lean?

A sinking foundation and improper planning are the reasons that the tower of Pisa leans to the side. Planning and preparation of the site of a construction project is tantamount to beginning to build the structure. An evaluation of the building site and analysis of the underlying ground structure will allow the construction plan to provide a firm base to hold up the structure. Improper planning will allow the finished structure to sink, break apart and/or crumble to ruin... just as it did with the Leaning Tower.

The designers of the structure failed to realize that the construction site of the tower and the foundation of the tower was marshy clay.

The construction was slated to be done in marble. After the first three floors of the tower were built, construction on the tower was temporarily halted due to the war that had broken out with Florence in 1178 and again in 1185. Then, another war began with Genoa in 1284. The tower construction remained on hold for about 100 years before the people of Pisa were able to return to the project. All the revenues of the city were required for the war effort and none could be diverted to the tower.

During the time of the wars when the construction was paused, the weight of the marble used in the first three floors of the tower caused the foundation of the tower to sink as the marshy clay settled. As the building project resumed, another four stories were added at a distinct angle to try to correct the sinking foundation. The correction wasn’t effective and the tower remained in a leaning state. The bells were attached in 1372 to the bell chamber on the top of the tower and construction was declared finished.

Continued Construction

In the 19th century, authorities in Pisa decided to dig a walkway around the base of the tower to allow visitors to appreciate the artisanship of the base. This removal of material only added to the lean of the tower.

During the 2nd World War, Mussolini gave an effort to straighten the tower. He ordered that the foundation be shored up by filling it with concrete to stop the foundation from sinking deeper into the clay. This effort was just as ineffective as previous attempts to arrest the rate of sinking. The concrete simply sank into the clay itself.

Correcting the Lean

Modern methods of correcting the instability of the leaning tower were also tried over the years. Counterweights, slings and excavated soil were installed to stabilize the tower.

Restoration work on the tower was performed in 1990 and 2001. Before the restoration, the angle of the lean of the tower was 5.5 degrees but after the restoration was completed, the lean was only 3.99 degrees.

In 2001, the leaning tower of Pisa reopened for visitors. One of the most popular activities involves climbing to the top of the tower and look out onto the landscape of the surrounding countryside. The top of the tower is 55.85 meters on one side and 56.70 meters on the other side. The tower leans 14 feet out of perpendicular now and is sinking about 1 mm per year.

Visitors who visit can now know that the tilt is caused by a combination of its enormous weight - over 14,000 tons - and by poor planning by the design engineers in 1173.

Notable Building Built to Show Success

The world famous leaning tower of Pisa, Italy is one of the most notable buildings in existence. Its construction was begun over 800 years ago. The intention of the building was to show to the world the prosperity of the town and its prowess as conquerors.

The skilled sailors of Pisa had conquered lands north as far as Norway, south into the African continent and east to Jerusalem. Their only real enemy at the time was Florence. The tower of Pisa was designed as nothing more than a bell tower for the city’s cathedral and a testament to the success of the society. The tower was to be an addition to the church buildings that included the Cathedral, the Cemetery, and the Baptistery.