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Italy's Pisa Tower Declared Stable August 25, 2004

The Pisa Tower During Restoration

The Leaning Tower of Pisa has been given some 300 years more of life, Italian experts announced.
Reporting on the present conditions of the monument at the 32nd World Geological Conference in Florence, Italy, Turin University's Michele Jamiolkowski, president of the committee for the protection of the tower, said that the famous tilt has been finally halted. Straightened by half a degree, the monument has stabilized for the first time in more than eight centuries.

"Apart from seasonal, cyclic movements, the tower has been basically motionless since September 2003. We believe geotechnical stabilization has been achieved," Jamiolkowski told the conference.

Cyclic displacements include the tower heating up at sunrise and slightly leaning to the west before returning to the original position.

The restoration has made the tower safe for the next 300 years, an achievement unimaginable 12 years ago, when the monument was so far off of perpendicular that it risked collapsing.

The soft, sandy subsoil is what has given the 179-foot tower its lean since Bonanno Pisano began building it in 1173.

It first started to subside when it was only 30 feet high. Undeterred, masons continued the work, adding more levels and using columns of varying length in the vain effort to straighten the slant as the tower grew higher.

Pisa's most famous landmark was completed 180 years later, with the bell tower placed on top in 1350.

Since then, no fewer than 17 committees have debated on how best to correct the monument's increasingly drunken angle. The archives of the Opera Primaziale, the body responsible for the tower's care, are full of schemes proposed over the past 150 years.

The present scheme involved several experimental techniques, including putting 800 tons of lead counterweights on the side opposite the lean.

At the end, experts adopted the simplest and most intuitive solution: digging out some earth from the side away from the tilt to allow the tower to settle more evenly.

More than 40 drills were used to remove 38 cubic meters of earth, while the tower — 14,000 tons of intricately carved white marble — was steadied by steel cables attached to the first tier and anchored to the ground.

"The key point of the project has been finding out that a slight decrease of the inclination would have stabilized the tower," Carlo Viggiani of Naples University commented.

Closed since January 1990, after experts noticed that its inclination had increased at a rate of 1 millimeter a year, the straightened tower reopened to the public on Dec. 15, 2001.

Guided tours of 30 people at a time are allowed to climb the 294 steps up the spiral stairway to the bell chamber.



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