Construction on the tower began in 1173 and it started listing soon after as it settled on soft soil. Over the centuries labourers and engineers tried to compensate for the lean but none of the measures succeeded . In 1990 the tower was closed to the public when a similarly constructed tower in Pavia collapsed. An international team devised a plan that included steel bands and lead weights and extracting soil from beneath the tower's northern foundation. It appears to have worked, at least for the time being. Engineers predict the structure will remain stable for at least another 200 years.
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