Mary Ann Adamko, age 11, of Herkimer, N. Y., for her question:
What caused the tower of Pisa to lean?
The famous white marble tower stands near the Italian river Arno some six miles from the Ligurian Sea a blue arm of the blue Mediterranean In the Middle Ages, Pisa was a city state whose territory reached from Genoa in the north down the western coast of Italy almost to Rome. Pisa also ruled the nearby Mediterranean islands of Corsica and Sardinia. The great wealth of the city state came from its mighty trading fleet.
Among its art treasures was a beautiful cathedral in the Romanesque style of architecture with slender columns topped with neat half circle arches, At the height of Pisa's power, in 1174, a bell tower was begun near the cathedral. It was to be a. round tower, also in the Romanesque style, made entirely of white marble. The plan called for a series of round galleries, one upon another, each with slender columns topped with neat round arches.
Nowadays, construction engineers examine the soil on which they plan to build. Then they put in strong foundations to help the ground to support the building. The great cathedrals and other buildings of the Middle Ages were built simply sitting on the ground with little or no foundation below ground. Many of these buildings still stand for two reasons. The ground chosen, perhaps by sheer luck, was solid enough to support them and did not give way under the weight. The architects knew a great deal about the weights, checks and balances which made a building stand solidly as a law unto itself.
The builders of the leaning tower were unlucky. When three galleries were completed, the structure began to tip. They were building on sand and the sand shifted, Rather than choose another site and start over„ it was decided to change the plans for the tower. The architects hoped to compensate for the shifting foundation.
The lower galleries were made extra firm. Their walls are 13 feet thick all of solid white marble. On these strengthened lower galleries, the tower was completed in 1350. There are eight of the graceful galleries reaching to a height of 179 feet the height of a 15 story modern building. A winding stairway of 300 white marble steps leads to the top gallery where the view is magnificent in all directions,,
But, because the foundation is not sound, the beautiful tower continues to lean further and further from the perpendicular. Pisa was the birthplace of the great scientist Galileo, He used the 1 aning tower to try to puzzle out some of the laws governing the speed of falling bodies.
Today, the great tower leans 162 feet from the perpendicular. If a heavy object is dropped from the top on the dipped side, it strikes the ground 162 feet from the base of the tower. Records show that the tower has tipped one foot in the past century which is why some architects call it the falling tower of Pisa.