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The Science Behind The Leaning Tower Of Pisa

August 30, 2021    7 min read

Did you know that the name of the town of Pisa comes from a Greek word meaning ‘marshy land’? Yeah, neither did the architects who were involved with constructing a spectacular monument in the 12th century. The existing church was renovated and enlarged, and a great domed baptistery was built on the plaza. Construction of a free-standing campanile, or bell tower, began in 1173. The monument, known today as the Leaning Tower of Pisa, gave architects the worst of headaches until the 20th century.

Source: Shutterstock

The Tower’s first architects thought that a three-foot deep foundation would be sufficient for an 8-storey monument, oblivious to the fact that the ground underneath the coastal city was marshy, made of clay mud and wet sand. Less than 5 years later, the south side of the tower was already underground. The pressure from the top levels would sink the structure and increase the lean if workers added more weight. So, what did they do then? Answer – they gave up.

Construction was halted for over a century due to wars in Italy, giving the soil time to settle. In 1272, architect Giovanni di Simone compensated for the minor tilt by making the next few stories higher on the south side, which led to it sinking even further. It does sound laughable now, but over a millennium ago, this seemed like the best option to straighten the Tower. By the time they completed the seventh floor and bell chamber, the angle of the tilt was 1.6°. Famous architects and engineers from all over the Roman Empire were called to Florence to try their hand at straightening the Tower. All they could do was ensure it sank further and tilted even more.

Fast forward to 1838, when a group of engineers dug a walkway around the Tower to examine the tilt. However, removing the supporting sand made the tilt worse. Then, in 1935, the Italian Corps of Engineers pumped mortar into the base to stabilize it. The mortar was not evenly dispersed across the foundation, resulting in yet another dramatic drop. No matter what anyone did, it just sank deeper into the marshy ground. Why? Because all these brilliant architects and engineers failed to realise the quality of the soil underneath the city.

Various architects after that tried to straighten the tower, leading it to sink more, until 1990, when the tower was leaning at an angle of 5.5°, almost on the verge of being toppled. In 1992, the team of engineers assigned the task of straightening the Tower drilled diagonal tunnels to remove 38 cubic meters of soil from under the tower’s north end. Then, they temporarily counterbalanced the structure with 600 tons of lead ingots before anchoring the base with steel cables.

Source: Shutterstock

The monument could finally be straightened. But now nobody wanted to lose the most famous feature of the Tower of Pisa, its tilt. The base of the monument was strengthened while also maintaining a lean of 4°, while also ensuring it would stay intact for another 300 years.

After all, where else could tourists click forced perspective photos of themselves kicking the famous Tower?

Source: Shutterstock

To find out more about the physics of how monuments lean or how gravity acts, sign up on the Practically app today! Amazing 3D videos, AR experiences, and life-like simulations await you! Stay tuned for more fascinating facts about the world around us.

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