The marble tower in Pisa, Italy, is a peculiar tower leaning to one side. In addition, Galileo discovered the law of free fall by doing experiments in this tower, so he is famous all over the world. Why is there this tower? Tracing back to the source, the construction of the leaning tower of Pisa began on August 9, 19741/kloc-0, and its inclination was caused by the negligence of the building. When the tower was built, it was also straight, but by the third floor, the structure was tilted. The main reason is that architects don't know much about the geological structure, the soil strength is poor, and the tower built with marble is heavy and high, and the foundation is only 3 meters deep, which causes the uneven sinking of the tower. The project was forced to stop. 170 years later, people continue to build. In order to prevent tilting, try to shift the center of gravity of the tower. However, the inclination of the tower bottom 3 has become a fact, so after the completion of the whole tower, the distance between the tower center and the vertical centerline is still 2. 1 m, and the tower body is still inclined with the passage of time. According to the measurement, from 1829 to 19 10, the annual average dip angle is 3.8 mm. It is estimated that it will collapse around 1965. Starting from 1978, the tilt almost stopped again.