The leaning tower of Pisa is made of white marble quarried from mountains close to the town. The tower began its famous lean about the time that the second story had been built. It took 199 years to complete the tower.
The reason for the tower's tilt is the soft ground beneath it and the fact that the builders didn't know how to create a firm foundation to keep the building level and plumb. Though efforts have been made to keep the tower from toppling, the tilt is considered a tourist attraction and maintained. The tower, whose architect was Bonanno Pisano, was supposed to be the bell tower of the cathedral of Pisa.