The Leaning Tower of Pisa, 185 ft. tall, was completed in 1370. The first foundation was set in 1173. In 1178, the tower was three-four stories high and building had been put to a halt due to lack of funds. [a] Once construction began a century later, builders noticed it had developed a slight lean to the north. This lean then continued from north to northeast, and finally south.
Construction was once again halted and resumed in 1272. At this time, counterweights were added to help prevent the building from leaning. Also, the builders put taller pieces of stone on the south side and shorter on the north side. However, unknown to the builders at the time, the tower was constructed on an old river delta. Because of this, the foundation underneath was made of soft sand and silt, causing the building to sink into the soil. [b] The tower tilts to the south because the soil under the south side is more compressible than the soil under the north. [a]
Since 1911 when measurements of the lean began, the tower has shifted approximately one twentieth of an inch per year, causing a displacement of 15 feet from vertical at the top. There have been many strategies taken to fix the lean, some doing more harm than good. For example, once the base of the ground columns were pushed underground, Alessandro Gherardesca dug into the ground in order for visitors to see the columns as they were intended to be seen. “He dug down about one and a half to two meters down straight into an area where a water table existed. Water came spouting out of the ground and the top of the Tower moved three quarters of a degree south. [a]”
Although this is regarded as failure, it has led to immense amount of attention for the small town of Pisa, and help during Galileo’s exploration of gravitational forces. [a]