Susie Gow, age 11, of Montreal, Que., Canada, for her question:
WHAT CAUSED THE TOWER OF PISA TO LEAN?
Nowadays, when you put up a building we must get a legal permit. And the soil must be tested to prove that the ground below is a safe place to begin. It's too bad that such permits were not needed in the 12th century. Otherwise, the famous Leaning Tower of Pisa might be standing tall and straight.
In the 11th century, Pisa was a booming Italian port. The people were proud of their ships and their trade and wealthy enough to plan magnificent buildings. In 1060, work was started on a splendid white marble cathedral. Almost a century later, work began nearby on a matching baptistery.
In 1174, this bustling town was ready to build a campanile, a bell tower to chime the hours and call the people to worship in their magnificent cathedral. A master builder named Bonanno was appointed to design and supervise the work.
His elaborate plans called for a stately, eight story round tower of white marble. Each story was to be an arcade of pillars and graceful arches. The plans were superb, but, alas, nobody tested the ground to make sure that the rocky layer below the surface was sturdy enough to support the masses of marble. As the second story was set up, the builders saw that the foundation was tilting to one side. The ground below this side was a buried layer of sand and water soaked clay.
Bonanno changed his plans to add extra weight to the nontilting side hoping to straighten up the structure. But the tilting continued as the fourth story was set in place. Work was stopped for 60 years or so, while experts debated the problem. Then the final stages were completed and the Leaning Tower of Pisa became a famous landmark, attracting tourists from far and wide.
Every year, the famous tower leans a tiny bit more and the top floor now hangs 14 feet out from the base below. True, one day it just might topple over, and some people laughingly call it the Falling Tower of Pisa. However, it is not likely to fall in the near future. And if there is solid bedrock below the weak sand, the famous tower may finally settle and tilt no further visitors who climb to the top get a sort of dizzy feeling. But the great Galileo made the best of the tilting tower. He dropped pebbles and feathers from the top to discover whether lightweight objects fall faster than heavier ones. In the meantime, the leaning tower has stood through many centuries and is not likely to topple next week or next year if at all.