Torre Pendente di Pisa
Location: Pisa, Italy
Built: 1173-1350
Architect: Unknown. The tower may have been designed by Bonanno Pisano and Guglielmo of Innsbruck, Austria or Diotisalvi.
The Tower of Pisa was designed as a bell tower but its main purpose was to promote the town of Pisa. 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. 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.
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 Tower of Piza leans at a 3.97 degree angle.
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