Was the Leaning Tower of Pisa Ever Straight?

 The short answer is no. It was never straight. 

But it is more interesting than that.

But first, what is the Leaning Tower of Pisa?

The Leaning Tower is the bell tower of the Duomo Square, a religious complex. 

The construction of the tower began in 1173 but the location was not ideal. The land was, and still is, spongy - AKA wet.  As a result, the structure began to noticeably lean not long after construction began. The builders noticed the issue while working on the third floor. But, then a war broke out among the Italian city-states. This delayed further work on the tower by about a century and allowed the base to settle. This abandonment may have prevented it from collapsing at the time.  The engineers attempted to compensate for the lean when construction began again. One method was making the stories slighter taller on the shorter side. But, the extra masonry added weight which caused more sinking. The tower was completed in 1372.

Leaning Tower of Pisa, 2022

Over the next four centuries, the tower's seven bells were installed. The heavier bells have been silenced due to fear their movement could affect the lean. The heaviest bell is nearly 8,000 pounds!

So the tower was curved from the beginning and will remain curved, even if the base became completely level. 

But, that does not mean the tower is standing with no support.

1990's Concerns

The tower was shifting at a rate of 1.2 millimetres per year, leading to concerns over its stability and future. In 1989, John Burland, a soil-mechanics expert, now an emeritus professor at Imperial College in London, led a team aiming to stabilize the tower. In 2018, he told Scientific American, "No matter how many calculations we made, the tower should not have been standing at all. . . The height and weight coupled with the porous soil meant it should have fallen centuries ago." He is still unsure how it remained standing until 1989. What he was sure of, was the tower would not have lasted much longer without intervention.

Their restoration work began in 1992.

In 1992, the north side of the base had sunk, leading to a 5.5 degree slope. When their work ended in 2001, they had reduce the slope to about 5 degrees. This still meant the tower was 13 feet away from being straight. If you are interested in reading more about their work, Scientific American and Leaning Tower Pisa have more information. 

Engineers measure the lean every year and interestingly, between the finish of the restoration project in 2001 and 2013, the tower has corrected itself a further 4 centimeters. 

While the spongy ground has caused the lean, it also helped the tower survive four major earthquakes as the soil enabled the structure to absorb the shocks. 

Is the Leaning Tower of Pisa in danger of falling?

In the 1990's that was a big fear, hence the major project to stabilize it. In 2005, an assessment declared the tower was stable for the next 200 to 300 years. While some engineers believe the tower will continue to straighten out and could be straight (or as straight as it can get) in the future, it will not be for a very long time. 

So if you want to visit it, you still have time.

Hughes, Rebecca Ann. "How the Leaning Tower of Pisa's Famous Tilt is Being Straightened." Forbes. December 30, 2022. https://www.forbes.com/sites/rebeccahughes/2022/12/30/how-the-leaning-tower-of-pisas-famous-tilt-is-being-straightened/  

"Leaning Tower of Pisa." Britannica. July 22, 2024. https://www.britannica.com/topic/Leaning-Tower-of-Pisa

Nadeau, Barbie Latza. "Leaning Tower of Pisa Corrects Itself. . . A Little." Scientific American. November 30, 2018. https://www.scientificamerican.com/article/leaning-tower-of-pisa-corrects-itself-a-little/