The Tower of Pisa ~ Why Does it Lean?


The Tower of Pisa ~ Why Does it Lean?

Have you ever wondered why the world-famous Leaning Tower of Pisa appears to be in danger of falling over? Is the angle at which it leans to the side intentional or accidental?

The tower is the campanile, or freestanding bell tower, of the cathedral in the Italian city of Pisa. It stands behind the cathedral and is the third-oldest structure in Pisa’s Cathedral Square (the Cathedral and the Baptistry are older). It’s tilted at an angle of 3.99 degrees and stands 183 feet high on the lowest side and 186 feet high on the highest side. That is roughly equivalent to the height of an 18-story building.

Construction on the Tower of Pisa was begun in August of 1173, during a period of military success and prosperity. By the time the very slow construction had progressed to the third floor in 1178, the tower began to sink because of a poorly constructed foundation that was set in unstable subsoil. The Republic of Pisa was by this time engaged in wars with Genoa, Lucca and Florence, so construction was halted for almost a century. (Can you imagine a construction project being halted for a century nowadays?) This century-long delay allowed for the soil to settle; if not, the tower would almost certainly have fallen over.

Construction was resumed in 1272 under the architect Giovanni di Simone. To compensate for the tilt, engineers began building upper floors with one side taller than the other, making the tower lean in the other direction. Because of this, the tower is actually curved. In 1284, construction was halted again when Genoa defeated the Republic of Pisa in the Battle of Meloria.

In 1319, the seventh floor of the tower was completed, but the chamber where the bells were housed was not added until 1372. There are seven bells in the tower, one for each note of the musical major scale. The largest bell was installed in 1655.

The Italian government in 1964 requested aid in keeping the tower from falling over, but, whatever measures were taken to keep it standing upright, the tilt that had become so famous had to be preserved. An international task force of engineers, mathematicians, and historians was assigned to study and analyze the problem. A period of structural strengthening to halt the ever-increasing tilt began in 1990 and lasted about eleven years, after which the tower was declared stable for at least another 300 years. Today the tower is undergoing gradual surface restoration to repair corrosion and blackening caused by wind and rain.

The Leaning Tower of Pisa remains a popular tourist destination for anyone fortunate enough to be traveling in Italy. Seeing the tower and going to the top of it is surely an experience not to be forgotten.

Copyright © 2012 by Allen Kopp

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