The Leaning Tower of Pisa was not intentionally built in a tilted shape at the very beginning of its construction, but was inexplicably tilted in the process of construction. After expert research, it was found that the Leaning Tower of Pisa tilted because of the special characteristics of the soil below its foundation. There are several layers of soil of different materials under the Leaning Tower of Pisa, formed between various deposits of soft, powdery soil and very soft clay, and at a depth of about one meter is a layer of groundwater. This conclusion was reached after observations were made of the composition of the foundation soil layers. Recent excavations have shown that the bell tower was built on the edge of an ancient coast, so the soil was sandy and sunken at the time of construction.

But a project in 1838 caused the Leaning Tower of Pisa to suddenly tilt at an accelerated rate, and emergency maintenance measures had to be taken. The architect Alessandro della Gherardesca excavated around the originally sealed foundations of the Leaning Tower in order to explore the shape of the foundations and reveal whether the column bases and foundation steps were as envisioned. This act caused the Leaning Tower to lose its original equilibrium, the foundations began to crack, and worst of all, an influx of groundwater occurred. Surveys after this work showed that the tilt had increased by 20 centimeters, whereas the previous 267 years of tilting had totaled no more than 5 centimeters.

After the end of the project in 1838, the accelerated tilt of the Leaning Tower of Pisa continued for a few more years, and then stabilized, reducing the tilt to about 0.1 centimeters per year, with the tower deviating from its "natural position" by more than 5 meters.