The leaning tower of Pisa was started at 1 174 and completed at 1350, all made of marble. The tower was erected at the beginning of construction, but when it was built to the third floor, the tower began to tilt and sink due to the shallow foundation and low strength of the upper floor, and the project was suspended. 1994, and a series of anti-tilt measures were strengthened. After more than 600 years of wind and rain, this tower stands tall and is famous all over the world.