Leaning Tower of Pisa Audioguide App

The architecture

Apart from its famous tilt that seems to defy the laws of gravity, the Leaning Tower of the Cathedral of Pisa is a very unusual building. The historical value of its design as well as its peculiar location within the vast and equally unique Piazza dei Miracoligive it a special place among Italy's many noteworthy sites.

The building is located at a distance from the Cathedral, between the apsidal area and the south-eastern section of the transept of the Cathedral. This is an unusual location. Normally, the tower would be erected near the facade or along one side of the church. In this case, however, the location of the tower has special significance because of its relationship to the other monuments of the Piazza dei Miracoli.

With its remarkable height and slim body, the Tower of Pisa was in fact perfectly visible from every part of the square and probably also from the river Arno. A veritable focal point, the Tower connected the city with the suburban location of the cathedral square. It stood as a beacon, a landmark, a lookout, and finally as an authoritative symbol of the civic and religious pride of the local community.

The building

The current building is the result of time-consuming construction work. It was restored several times through the centuries, mostly to reduce the risk of collapse as a consequence of its remarkable inclination.

The edifice is composed of a cylindrical stone body surrounded by open galleries with arcades and pillars resting on a bottom shaft, with the belfry on top. The central body is composed of a hollow cylinder with an outer facing of white and gray San Giuliano limestone, an interior facing (also made of textured "verrucana" stone), and a ring-shaped stone area in between. This stone area accommodates a winding staircase with 293 steps leading up to the sixth open gallery. There, the inner shaft is closed by a vault with a central hole to let light in. From here, you can access the belfry, as well as the lower mezzanine floors and the open galleries.

The Tower of Pisa is divided into eight segments which are called “orders.” A circle of blind arcades placed on half columns enhances the lower order. A diamond-shaped compass inlaid with polychrome marble with a raised rosette in the middle is placed under the arcade. The openings of some narrow single-lancet windows interrupt the solid wall.

The only entrance door creates an opening to the west: a rectangular area framed by a lintel. Above the lintel, a crescent-shaped arch with an inlaid archivolt rests on two capitals as a continuation of the jambs, forming a shrine containing the bust of a 14th-century Virgin with Child. On either side of the door, friezes featuring animals, monstrous figures, and the unusual shapes of some ships (maybe representing the port of Pisa) frame the commemorative epigraph of the foundation of the building.

The inclination

The problem of the inclination is one that has most fascinated and intrigued visitors, art lovers, and experts over the centuries. It is the feature that has made Tower of Pisa so famous all over the world. Adding to the appeal is the fact that the reasons for the inclination of the building are still fairly mysterious.

Experts have asked, whether the incline of the Tower of Pisa is an effect the builder deliberately wanted to achieve. Or, was it the consequence of an unpredictable and unavoidable, progressive subsidence of the ground?

Increasingly accurate measurements of the building and surveys of the subsurface have shed some light on the matter during the last century.

The Tower was presumably initially designed as a straight building. However, it began to sink right from the first stages of the building work. The subsidence was due to the special morphological features of the ground, which is composed of several layers of clay and silt, with groundwater levels running through it at about one meter in depth.

Based on the little information we have, we do know that the oscillation of the building was minimal over the centuries, as it seems to have settled. This fact is corroborated by the survey conducted in 1817 by two English experts, Cresy and Taylor.

A few years later, in 1838, some event must have occurred which abruptly accelerated the oscillatory motion of the building, necessitating major protective work. Based on historical and artistic considerations, it was decided to clear the bottom of the tower of the mantle of soil that had been hiding it for centuries. This involved the demolition of the buildings and constructions next to the Tower as well as draining the brackish water that surrounded the entrance of the building. This intervention caused the Pisa Tower to lose its balance.

The subsequent measurements showed that the inclination of the Tower of Pisa had increased by approximately 20 centimeters. In the 267 years between Giorgio Vasari’s surveys in 1550 and those of the two Englishmen in 1817, the inclination had increased by just five centimeters. The leaning movement kept accelerating for a few years after the work of 1838, then decreased again to about one millimeter a year.

During the 20th century, deeper understanding and better technical instruments, along with the support of governmental and safety authorities led to a proliferation of studies, surveys, and special projects.

The measurements of the Tower of Pisa

The monument is 58.36 meters high at the foundation and over 55 meters above ground. Its weight has been calculated at 14,453 tons. The center of gravity is 22.6 meters above the foundation plane. The outer diameter of the foundation measures 19.58 meters; the central hole is 4.5 meters wide. The area of the ring-shaped foundation covers therefore 285 square meters; the average pressure on the ground is 497 kPa. The current inclination is approximately 55°, i.e. approximately 10%. The eccentricity of the load on the foundation plane is 2.3 meters.