Leaning Towers, From Pisa and Beyond

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The Tower of Pisa

Leaning Tower of Pisa and Duomo de Pisa, Piazza dei Miracoli, Pisa, Tuscany, Italy
Leaning Tower of Pisa and Duomo de Pisa, Piazza dei Miracoli, Pisa, Tuscany, Italy. Photo by Martin Ruegne/Radius Images Collection/Getty Images

Most tall buildings stand up straight, but sometimes things go wrong. These three buildings seem about to collapse. What holds them up? Read on...

The Tower of Pisa in Pisa, Italy is one of the world's most famous leaning buildings. Going by the names of Torre Pendente di Pisa and Torre di Pisa, the Tower of Pisa was designed as a bell tower (campanile) but its main purpose was to visually attract people to the cathedral in the Piazza dei Miracoli (Miracle Square) in the town of Pisa, Italy. The foundation of the tower was only three meters thick and the soil underneath was unstable. A series of wars interrupted the construction for many years, and during the long pause, the soil continued to settle. Rather than abandon the project, builders accommodated the tilt by adding extra height to the upper stories on one side of the Tower. The extra weight caused the upper part of the Tower to lean in the opposite direction.

Construction Description: You can't tell just by looking at it, but the Tower or Pisa is not a solid, room-filled tower. Instead, it is "...a cylindrical stone body surrounded by open galleries with arcades and pillars resting on a bottom shaft, with the belfry on top. The central body is composed of a hollow cylinder with an outer facing of shaped ahlars in white and grey San Giuliano limestone, an interior facing, also made of textured verrucana stone, and a ring-shaped stone area in between...."

The Romanesque style bell tower, built between 1173 and 1370, rises to a height of 191 1/2 feet (58.36 meters) at the foundation. Its outer diameter is 64 feet (19.58 meters) at foundation and the width of the center hole is 14 3/4 feet (4.5 meters). Although the architect is unknown, the tower may have been designed by Bonanno Pisano and Guglielmo of Innsbruck, Austria or Diotisalvi.

Over the centuries there have been many attempts to remove or reduce the tilt. In 1990, an Italian government-appointed special commission determined that the tower was no longer safe for tourists, closed it off, and started devising ways to make the building safer.

John Burland, a professor of soil mechanics, came up with the system of removing soil from the north side in order to make the building settle back into the ground and thus reduce the tilt. This worked and the tower was reopened to tourism in 2001.

Today, the restored Tower of Pisa leans at a 3.97 degree angle. It remains one of the top tourist destinations of all the architecture in Italy.

Learn More:

  • Burland J.B., Jamiolkowski M.B., Viggiani C., (2009). Leaning Tower of Pisa: Behaviour after Stabilization Operations. International Journal of Geoengineering Case histories, http://casehistories.geoengineer.org, Vol.1, Issue 3, p.156-169 PDF

Source: Miracle Square, Leaning Tower, Opera della Primazial Pisana at www.opapisa.it/en/miracles-square/leaning-tower.html [accessed January 4, 2014]

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The Tower of Suurhusen

Leaning Tower of Suurhusen in East Frisia, Germany
Leaning and Lopsided Buildings: The Tower of Suurhusen in East Frisia, Germany Leaning Tower of Suurhusen in East Frisia, Germany. Photo (cc) Axel Heymann

The Leaning Tower of Suurhusen in East Frisia, Germany is the most tilted tower in the world, according to The Guinness Book of World Records.

The square tower, or steeple, of Suurhusen was added to the Medieval church in 1450. Historians say that the tower started to lean in the 19th century after water was drained from the marshy land.

The Tower of Suurhusen tilts at a 5.19 degree angle. The Tower was closed to the public in 1975 and did not reopen until 1985, after restoration work was completed.

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The Two Towers of Bologna

Towers of Bologna
Leaning and Lopsided Buildings: The Two Towers of Bologna, Italy The two leaning towers of Bologna, Italy are symbols of the City. Photo (cc) Patrick Clenet

The two leaning towers of Bologna, Italy are symbols of the City. Thought to be built between 1109 and 1119 AD, the two towers of Bologna are named after the families who had them constructed. Asinelli is the taller tower and Garisenda is the smaller tower. The Garisenda Tower used to be taller. It was shortened during the 14th century to help make it safer.