People wanted to build an imposing tower in Pisa in the Piazza dei Miracoli (Square of Miracles) in the twelfth century.

In 1173, construction of the tower of Pisa began. Five years later, by which time three floors had been built, the tower began to slope due to the soft ground. Because the people of Pisa came to war with Genoa and Florence, the construction of the tower was halted for about 100 years. This gave the ground time to harden. If the tower had been completed in one go, it would definitely have fallen over. In 1272, construction of the tower resumed and it was decided to use more mortar (a certain type of fine concrete) on one side than on the other to compensate for the crookedness of the first three floors. After this, construction again fell silent for about 50 years. Finally, in 1372, the last floor was built. This one was again built straight. Because this floor was built perpendicularly, the tower not only became tilted, but also crooked.

The tower has been threatened with toppling several times despite the architects' attempts to set it straight. Through expensive renovations - the last phase of the renovation cost a whopping 28 million euros - the tower has now been stabilized. The lean in 1993 was four and a half meters, now it has been reduced to four meters.