In 1172, Donna Berta di Bernardo donated sixty silver coins to the local cathedral for the purchase of stones to be used in the base of a new bell tower.
The next year, construction on the tower started and almost immediately there were some problems. The tower site that sat on soft ground composed mostly of clay, fine sand, and shells. By the time the builders finished the second floor in 1178, the tower was beginning to lean.
Soon, construction was stopped for almost 100 years, as Pisa fought wars against Genoa, Lucca and Florence. This may have been a good lucky break, as modern analysis says that the tower definitely would have toppled had construction continued without time for the soil to settle.
Over the next century, construction continued intermittently.