Construction of the famous white marble bell tower (campanile) of Pisa’s cathedral began in 1173 but by
the time three stories were built, it had already begun to lean. Over the centuries, many methods have
been tried to prevent the lean getting worse but as most people did not understand what was causing
the lean, they made it worse. The soil under the tower is very soft and waterlogged in parts, which is the
most plausible explanation for the lean. In 1990, the tower was closed to the public because cracks in
the walls were worsening and it was feared that it might topple over. Since then, straps and cables have
been used to hold it in place, 800 tonnes of lead weights have been added to the high side of the base
and 38 cubic metres of soil removed from that area, which has stabilized the tower, and even reduced
the lean slightly.