Thanks to the soft ground, it had begun to lean by the time its builders got to the third story, in 1178. Shifting soil had destabilized the tower’s foundations.
Over the next 800 years, it became clear the 55-metre tower wasn’t just learning but was actually falling at a rate of one to two millimeters per year.
Today, the Leaning Tower of Pisa is more than five meters off perpendicular.
Its architect and engineer tried to correct this by making the remaining stories shorter on the uphill side – but to no avail. It kept leaning more and more.
The lean, first noted when three of the tower’s eight stories had been built, resulted from the foundation stones being laid on soft ground consisting of clay, fine sand and shells.
The next stories were built slightly taller on the short side of the tower in an attempt to compensate for the lean. However, the weight of the extra floors caused the edifice to sink further and lean more.
