The Leaning Tower of Pisa: Why Does It Lean?

The Leaning Tower of Pisa: Why does it Lean?

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By Mr Ghaz, March 29, 2010

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The Leaning Tower of Pisa: Why does it Lean?

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The leaning tower of Pisa, in Italy is, one of the world’s most beautiful and bizarre buildings. Breaking every architectural rule, the tower at present leans about 14 feet from the vertical and continues to lean farther south every year. The structure, today more than 800 years old, has leaned almost since the day construction was started.

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In 1174, during Pisa’s golden age, a period of economic prosperity and artistic riches, the citizens resolved to build the campanile (bell tower) that their magnificent cathedral had been without for so long. The tower was to surpass all other towers being built in Italy at the time and was to symbolize the wealth and power of the illustrious Republic of Pisa.

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Decline – And Fall? The Leaning Tower of Pisa has been on a tilt since it was built more than 800 years ago. From the top of the tower, astronomer and physicist Galilei, a native of Pisa and lecturer in mathematics at the university between 1589 and 1591, conducted his famous experiments. He proved that bodies of different weight fall at the same speed.

Work in Progress

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The first stone was laid in August 1174, and numerous architects and master masons worked on the structure. But no sooner had the first story been completed, than the tower started to lean to the south. The culprit was settling of the foundation. To compensate, subsequent stories were built closer to the vertical in order to “straighten” the tower.

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The work was very laborious, and the architects and masons either lost interest or were defeated by the problem of the lean. Meanwhile, the tower continued to tilt badly. More radical solutions had to be found for the upper stories, or the whole tower would topple.

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One of the more ingenious solutions was to make the pillars on the south side higher than those on the north, so that the tower could “grow” back into line.

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The tower was completed in 1350, when the bell chamber was added-also built at an angle to compensate for further settling, with the heaviest bells on the north side. But the tower still leaned southward. Fortunately, no further stories were added. Had they been, the center of gravity would have moved outside the base of the tower, and the entire structure would have fallen.

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The site was the cause of all the problems. Pisa stands on a flat alluvial plain, and settling is a common phenomenon throughout the city.

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The famous Leaning Tower itself is cylindrical, with eight stories of arched arcades built of white marble. Its present height is 179 feet, although it was originally taller. Not only has settling caused it to lean but also has made it sink into the ground.

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Modern technology has helped to stabilize the tower and arrest its rate of lean to about one-sixteenth of an inch every year. But even at this rate, in another 175 years the tower will fall to the ground, reduced to a pile of rubble.

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