The Leaning Tower of Pisa began to tilt while it was being built

Builders began the freestanding bell tower for Pisa Cathedral in 1173. After they completed its first three levels, the soft ground beneath the shallow foundation settled unevenly: by about 1178 the tower had started to lean, and work stopped. Construction resumed decades later and finished around 1370. The upper levels were built with a slight curve in the opposite direction to partly compensate for the tilt.