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One of the most interesting things about the tower ( Torre Pendente in Italian) is that it has always tilted. Twelve years after work began, when it was only three storeys high, in 1173, the foundations began to sink on one side, but in the opposite direction from the current lean or rather in the same direction as the baptistry. Masons wedged in stones to correct the problem but this only caused the tower to tilt the other way and so work was halted. When the next storeys were added, they were tilted purposefully to counterbalance the lean and it went until in 1350 Tommaso Pisano completed the work with a lopsided bell-chamber. A couple of centuries later, Galileo exploited the overhang in one of his celebrated experiments, dropping items of different mass off the top to demonstrate the constancy of gravity. The first attempt to correct the lean consisted of digging a trench around the base of the tower but this only made things worse. In 1990 when the top leant more than five metres of its vertical, the tower was closed to visitors. Wrapping steel bands around the lowest portion of the tower continued to make matters worse and shift more in the first weeks of the fix than it normally did in a whole years. The next fix aimed at stabilizing the tower by shoring up its northern side with 800 tonnes of lead blocks piled at its base. The idea was to follows this with the insertion of cables into the bedrock and then wrapping them around the foundations but drilling into the bedrock beside the foundations made it more unstable and it lurched another couple of millimetres. The final solution was to remove silt and sand from beneath the foundations using an array of rotating drills that gradually worked their wasy around the tower while constantly monitoring the effect.This method has worked and the tower slowly began to correct its lean. By summer 2000, the tower had straightened by five degrees, or 15cm and was back to the position it had in 1870. The ead blocks are being moved one at a time underground to anchor the cables that are still in place and the tower is open once again to visitors. When all of the work is finished, the tower will still lean, otherwise why save it, but the way it did in Galileo's day so that we can enjoy it in its initial glory. |