2023-08-05 13:00:00
The foundation stone of what is probably the most well-known and striking sight in Italy was laid 850 years ago, on August 9, 1173. Nowadays, more than a million people make a pilgrimage to the historic building in Tuscany every year.
architectural history.
The “Torre pendente di Pisa” – that’s its original name – was planned as a free-standing bell tower (campanile) in the Romanesque style next to the city’s cathedral – perpendicular, mind you. Bonanno Pisano and a certain Guglielmo were probably among its architects. However, recent research suggests that Diotisalvi, the architect of the Baptistery on the opposite side of Pisa Cathedral, also designed the tower.
Twelve years after construction began, as workers were building the third floor, the truncated tower was slowly tilting toward the southeast. The subsoil of sand and loamy mud and a foundation that was only three meters deep were responsible for the sinking. In addition, the tower stands on the edge of a former island right next to an ancient harbor basin that was already silted up at the time of construction.
It was not until 1272 that the architect Giovanni di Simoni dared to continue building. He had the next four floors created with a lower angle of inclination. But the top bell storey could only be completed in 1372, instead of a planned height of 100 meters, only 54.80 meters were realized with a diameter of twelve meters. At the time of completion, the incline was almost two meters. One reason for the almost 200-year delay was probably the war between the independent city-state of Pisa and the Republic of Genoa.
The eight-story campanile weighs 14,500 tons and its facade is adorned with the famous white Carrara marble, which was also used for Florence Cathedral and St. Peter’s Basilica in the Vatican. Each floor has a gallery of 30 arcades. On the south side, six steps lead up to the belfry, on the north side only four. The seven bells, each of which has a different pitch, were not allowed to be rung for a long time because of the risk of them collapsing. In the meantime, however, they can be struck almost vibration-free using internal electromagnetic hammers and without the bells having to be made to swing. The tower also served as a place of refuge for the clergy in the event of external danger.
Legend has it that the city’s most famous son, Galileo Galilei, used the Leaning Tower for his groundbreaking studies. To prove that the rate of fall does not depend on mass, he dropped two cannonballs from the tower.
At the beginning of the 20th century, technical possibilities existed for the first time to measure the leaning of the bell tower with millimeter precision. In 1918 it deviated more than five meters from the vertical, since then the inclination has steadily increased. The ensemble on the Piazza del Duomo, which includes the tower, the cathedral and the baptistery, was declared a World Heritage Site by Unesco in 1987.
In order to prevent the tower from collapsing, experts from all over the world were asked in 1990 to come up with stabilization solutions. Initially, steel cables, 800-ton lead weights and steel tires were used. In 1995 the construction was replaced by a system of underground anchorages. At that time, the tower even defied an earthquake. “Ironically, the same soil that nearly collapsed the tower and made it askew is responsible for surviving every earthquake,” said George Mylonakis, an earthquake expert at the University of Bristol.
Finally, in the fall of 1998, four to five meter deep sloping holes were drilled into the ground beneath the northern part of the tower, removing about 50 cubic meters of material. As a result, the sandy soil was better distributed under the foundation and the incline was reduced by 44 centimeters from 5.5 to 3.97 degrees. The reopening took place on June 16, 2001. Since then, the stay has been limited to a maximum of 15 minutes, and only 40 people are allowed to visit the tower at the same time. You have to climb 296 steps to the top of the tower.
“We can now say that the tower is standing still and that it will remain so for at least the next 300 years,” says Michele Jamiolkowski, professor emeritus of geotechnics and chair of the international commission to save the Leaning Tower of Pisa from 1990 to 2001. Incidentally, with modern technology it would have been possible to erect the tower completely. But that was not the aim of the engineers, because who wants a straight tower of Pisa as a tourist attraction?
In addition to the leaning structure in Tuscany, there are a number of other towers that have an even greater inclination. Many are in Germany, and almost always yielding ground is responsible for their inclination. The leaning tower in Bad Frankenhausen, Thuringia, is part of the 630-year-old upper church. Due to the continued sagging in the salt and gypsum rock, the 56 meter high tower now has an incline of 4.93 degrees. With an overhang of 4.60 meters, it deviates more than half a meter from the perpendicular than its “competitor” in Pisa.
The 27 meter high tower in Suurhusen, Lower Saxony, was built in 1450 on a foundation of oak trunks. As they began to modernize over time, the tower today leans 5.19 degrees. In Dausenau, Rhineland-Palatinate, the almost 680-year-old tower of the town fortification is tilted by 5.22 degrees. Also in Rhineland-Palatinate there is a medieval defense tower in Gau-Weinheim, which was expanded in 1749 as a bell tower. According to a recent measurement, its inclination is 5.42 degrees.
However, the sloping tower in Germany is in Midlum in south-western East Friesland. The bell tower was probably built before 1300 and is considered one of the most leaning towers in the world with a tilt angle of 6.74 degrees. However, the Guinness Book of Records denied it a top position, since its height of only 14 meters is not a multiple of its diameter and it is therefore allegedly not a tower.
In December 2011, a multifunctional skyscraper was opened in Abu Dhabi in the United Arab Emirates with the Capital Gate designed by the British architects RMJM. 35 floors are spread over a total height of 160 meters. With an inclination of 18 degrees, it is the most inclined tower in the world, which, in contrast to the towers described above, was planned with full intention – as evidenced by perfectly horizontally aligned floors.
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