Leaning Tower of Pisa

The Leaning Tower of Pisa is a campanile, or bell tower, originally constructed from the 1100s to the 1300s to accompany the Pisa Cathedral in Pisa, Italy. A weak and shallow foundation caused the structure to begin leaning in the late 1170s, giving the tower the unique tilt for which it later became well known. Reconstruction in the 1990s and early twenty-first century made the tower safe for tourists to climb while maintaining its trademark lean.

History of the Tower

In medieval times, the city of Pisa on the coast of Italy's Tuscany region was a major trade center. Its power continued to increase into the 1000s CE, with the city's commerce and military fleet becoming dominant forces on the central Italian coast.

In medieval Italy, it was common for wealthy cities to build ornate bell towers to show off their robust economies. This was Pisa's position in the late 1100s, and as such, the city's administrators commissioned the construction of a tower near the Pisa Cathedral in the Piazza dei Miracoli, or "Square of Miracles."

The architect of the Tower of Pisa is not truly known, but it is generally believed to have been the engineer Bonanno Pisano. On August 9, 1173, he laid the tower's marble foundation ten feet into the ground. This depth was not ideal for the foundation of such a large structure, but the ground underneath contained a great deal of water and so was too soft to be dug any deeper. Between the water and the foundation, Pisano laid a thick clay mixture meant to hold the tower firmly in the ground.

The rounded bell tower would be made almost entirely of white marble blocks. Pisano built the tower's first floor to be taller than the others. The solid outer wall featured columns and arches all the way around as well as sculptures of animals and mythical creatures. The tower's entrance was set between two columns.

The Leaning Tower

The tower's second floor and all successive floors would look almost exactly like one another. Also constructed of white marble, they were to be open-air arcades, essentially hallways that wrapped around the outside of the rounded tower and were supported by numerous short columns.

The third level was completed in 1178, but by this time, the tower had begun to lean noticeably to the south. This was due to the faulty way Pisano had constructed the foundation. Only ten feet deep, the foundation was much too shallow to support the large tower, and the entire structure was now too heavy for the soft clay mixture underneath the foundation. As a result, the tower had crushed the clay and had begun to lean.

The builders attempted to correct this problem aesthetically by simply constructing the columns and arches on the sinking side taller than those on the other. By the time the workers reached the fourth floor, they were forced to make the columns even taller. This eventually proved impractical, as the tower continued to lean and seemed likely to fall in any case.

In 1185, therefore, the workers determined the safest way to continue building the tower would be to leave it alone until the whole structure sank into the lower position in the clay. However, while the people were waiting for the tower to correct itself, war broke out between Pisa and several nearby Italian cities. These were violent and expensive enterprises for Pisa, and the city could not continue constructing the tower until 1272.

Further Construction and Completion

By 1272, the Tower of Pisa's foundation had finally settled as the workers one hundred years earlier had hoped it would, though the tower continued to lean. The engineer Giovanni di Simone then took over construction of the tower's upper levels. As the workers of the previous century had done, Simone compensated for the tower's lean by building the arcade columns on the sinking side taller than those on the other side. However, after completing several floors, Simone noticed the tower had begun leaning even more and immediately stopped construction.

At this time, 1284, Pisa entered another war and did not resume building the tower for another several decades. The seventh floor was finished in 1319, while the bell chamber at the top was completed in 1372. Seven bells were later added to this chamber over the next several hundred years, each tuned to a different note of the major music scale. The finished Tower of Pisa comprised more than 14,000 tons of marble and stood 183 feet tall.

Modern Renovations

The tower underwent several renovation attempts throughout the twentieth century, all designed to keep the structure from eventually falling. Engineers determined in 1911 that the tower leaned another one-twentieth of an inch every year. In 1934, Italian dictator Benito Mussolini tried to repair the tilt by injecting two hundred tons of concrete under the tower's foundation, but this actually increased the lean.

True progress on saving the tower began in 1989, when the structure was discovered to be tilting 5.5 degrees from vertical. That year, another medieval bell tower suffering from a similar lean in Pavia, Italy, suddenly collapsed. These factors inspired the Italian government finally to correct the Tower of Pisa's tilt or risk seeing it destroyed.

The tower was closed to tourists in 1990 while a team working under British engineer John Burland began investigating what could be done. Burland eventually found that removing soil from under the tower's north side would allow the structure to settle more flatly into the ground.

After securing the tower by removing its heavy bells and wrapping steel support bands around the body, Burland's team drilled numerous holes under the foundation. They removed seventy-seven tons of earth from under the north side, and the tower then settled back to a 3.97-degree lean. The team also installed a drainage system to control fluctuations in groundwater levels, which exacerbated the tower's tilt. Upon completion, engineers declared the building would be entirely safe leaning at this angle, which they preserved to retain the building's unique cultural heritage. The Leaning Tower of Pisa reopened to the public in 2001. In 2018, it was noted that the tower had further corrected its lean by 1.5 inches (4 centimeters) and was continuing to settle due to the earlier restoration efforts. In the twenty-first century, this United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage Site remains one of Italy's most visited tourist attractions.

Bibliography

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"The Leaning Tower of Pisa: Flawed Beauty." The Museum of Unnatural Mystery, www.unmuseum.org/7wonders/leaning‗tower.htm. Accessed 14 Jan. 2025.

"Leaning Tower of Pisa History." Leaning Tower of Pisa, www.towerofpisa.org/leaning-tower-of-pisa-history/. Accessed 14 Jan. 2025.

Rice, Doyle. "Why Doesn't the Leaning Tower of Pisa Fall Over?" USA Today, 10 May 2018, www.usatoday.com/story/news/world/2018/05/10/leaning-tower-pisa-why-still-standing/598673002/. Accessed 14 Jan. 2025.

"Stabilising the Leaning Tower of Pisa." Institution of Civil Engineers, www.ice.org.uk/what-is-civil-engineering/infrastructure-projects/stabilising-the-leaning-tower-of-pisa. Accessed 14 Jan. 2025.