The Leaning Tower Of Pisa Isn’t Leaning So Much Anymore … Here’s Why

It’s an iconic landmark that put the town of Pisa, Italy, on the map. But the world-famous Leaning Tower was on the verge of collapse near the end of the 20th century before a crew of experts started working on a plan.

Before we get there, let’s explore what gave the building its lean in the first place.

Underground uncertainty

For millions of years, a river flowed into the Ligurian Sea, causing it to rise and fall while changing the makeup of the nearby soil. This was concentrated in the area of Pisa, where a mismatch of sand and clay made for a sketchy foundation when construction of the tower began in the 12th century.

It kept leaning more and more until 1990, when its 5.5-degree tilt sparked calls for immediate action. The previous year, a similar building collapsed, and the Italian government knew something needed to be done.

A complex solution

Engineers and architects performed a series of tests to determine the best way to reverse course while preserving the trademark lean that brought so many tourists to the town.

They started with a temporary stabilization method that worked for a while as they started to research more permanent fixes. Pumping groundwater from the sand would have unpredictable results and electro-osmosis to remove water from the clay didn’t really work on the highly conductive material.

In the end, they divided to selectively excavate the ground. Starting around the turn of the 21st century:

• 41 long holes were dug underneath the tower
• About 70 tons of soil were removed altogether
• The tower’s tilt was reduced by about half a degree

This put the tower at about the same lean as the early 19th century, meaning it’s once again safe from collapse (at least for now).

Chris Agee December 21st, 2023

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