Leaning Tower of Pisa: Facts & Figures

We can’t even put a number on the pictures of people we’ve seen “holding up” the tilted tower. Well, not just people, we recently saw a trending picture of a cute little dog “holding up” this unique piece of architecture, on social media! Even with its flawed appearance, the Leaning Tower of Pisa is still one of the world’s most beloved architectural monuments. This famous tourist spot has been leaning for nearly 840 years now! Its story started from the very beginning of its construction.

The Leaning tower of Pisa Location:

Standing within the Piazza Dei Miracoli, Pisa, Italy; the Tower of Pisa is part of the complex of four gleaming white medieval buildings, comprising the Cathedral (Duomo), its bell tower (the Tower of Pisa), its Baptistery and the Cemetery (Camposanto).

Image by Makalu from Pixabay

The Basic Structural Details:

  •  Built in Romanesque style of architecture, this eight-storey tower stands 54.7 m high above ground level. The bell chamber has Gothic elements of belfry infused with the overall style of the tower. Articulated by engaged columns with classical Corinthian capitals, the ground floor of the tower is a series of blind windows.
  • The tower is in the form of a hollow cylinder. It is surrounded by colonnades, with a spiral stairway winding up within the tower.
  • The structure weighs about 14,500 metric tons. Its masonry foundations are 19.6 m in diameter with a maximum depth of 5.5 m below ground level.
  • The structure’s foundation slopes towards the south at 5.5 degrees to the horizontal. Also, the seventh floor overhung the ground by about 4.5 m.
Photo by Alex Ghizila on Unsplash

Two Centuries of Construction:

The stabilization of the Leaning Tower of Pisa had been immensely challenging for the engineers and architectural conservationists. One of the most fascinating Leaning Tower of Pisa facts is that the structure did not start leaning after its complete construction. Since the constructions of the tower began in August 1173, it had been under the danger of collapsing.

Photo by Victor He on Unsplash
  • The constructions of the tower had to be stopped in 1178, when the tower had progressed to the fourth storey. The foundation of the structure began to settle unevenly on soft soil composed of mud, sand, and clay. As a result, the structure started leaning slightly to the north.
  • After almost 100 years, the work was re-commenced in 1272. By this time, the soil under the foundation had subsided unevenly. Due to this, the tower had tilted to the south; however, it had also increased the strength of the clay due to consolidation under the weight of the tower.
  • By 1278 the construction had reached the seventh level when the work had to be stopped again. It is said that if the Tower had been completed at this stage, it would have fallen over!
  • In 1360, further consolidation of the underlying clay had taken place. Work on the bell chamber was further commenced by this time and was finally completed in 1370!

It took nearly 2 centuries after the commencement of construction to complete an after all “Leaning” Bell Tower!

Leaning tower of Pisa: Why was there a Need of Correction?

After the first phase, up to the fourth storey, the tower was leaning towards the north by about 0.25 degrees. In an attempt to correct the lean, tapered blocks of masonry had been used at each floor to bend the axis of the Tower away from the lean.

  • Thereafter, as the construction advanced above the fourth storey, by constructing one side taller than the other. As a result, the Tower started tilting towards south. By the time it reached the seventh level in 1278, the tilt had increased to about 0.6 degrees southwards.
  • This rapidly increased to about 1.6 degrees by 1360 when the work of the bell chamber commenced.
Photo by hitesh choudhary from Pexels

Further tilting – Interesting Leaning Tower of Pisa facts:

  • During the late 16th century, Galileo Galilei is said to have dropped two cannonballs of different masses from the top of the tower, it was observed that the Tower had moved about 3 degrees off vertical.
  • In 1817, two British architects used a plumb line to measure the inclination and found out that it had increased to 5 degrees, implying that the bell chamber’s construction had caused a very significant increase in its inclination.
  • During 1838, architect Alessandro Della Gherardesca excavated a walkway around the base of the Tower to reveal the tower’s plinths and foundation. As a result of which there was an inrush of water on the south side which further worsened the tilt.
  • Precise measurements begun in 1911 and they showed an increasing rate in the tilt of the tower. The rate of the tilt had doubled since the mid-1930 and by 1990 it was stated that the rate was equivalent to a horizontal movement at the top of about 1.5 mm per year! Moreover, any interference with the Tower had been resulting in significant increases in the tilt which confirmed how delicate any method of stabilization would have to be.

‘Why is the Leaning Tower of Pisa leaning?’ is one of most googled questions and these facts certainly explain the curiosity.

The Mission to Stabilize:

In 1990, the Leaning Tower of Pisa location was closed to the public. It was enforced due to safety concerns and increasing harm to the structure. In the same year, a commission was established by the Italian Prime Minister to implement stabilization measures for the tower.

  • Stabilization was achieved by an innovative method of soil extraction. This caused a small reduction in the inclination of the tower which is not visible to the casual onlooker.
  • This technique has provided an ‘ultra-soft’ technique of increasing the soundness of the Tower. This, at the same time, fulfills the requirements of architectural conservation.
  • The whole process required advanced computer modeling, large scale development trials, and an exceptional level of continuous monitoring, and daily communication and control.
  • By 2001, the team had decreased the tower’s lean by 440 mm. Thereafter, it was finally re-opened on 15th December 2001.  

There are still a few potential problems like that of the material in the lower floors of the tower, where most of the forces caused by the century-long leaning have been directed. If any of this masonry crumbles, the tower would collapse too. Even a minor earthquake could have similar consequences. However, despite these problems, the engineers expect this unique leaning tower to sustain its stability for another 200 years!