Why is the Tower of Pisa leaning?

In 1172, Donna Berta di Bernardo donated 60 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 began and almost immediately there were problems. read more

The Leaning Tower of Pisa (Italian: Torre pendente di Pisa) or simply the Tower of Pisa (Torre di Pisa [ˈtorre di ˈpiːza]) is the campanile, or freestanding bell tower, of the cathedral of the Italian city of Pisa, known worldwide for its unintended tilt. read more

The straightening continued after the tower reopened in 2001, and in 2008 sensors showed the subsiding motion had stopped, after a total improvement of some 19 inches. Engineers now believe the Leaning Tower of Pisa will remain stable for some 200 years, barring an earthquake or other unpredictable disaster. read more

When work on the tower resumed again, it was leaning 0.2 degrees north of vertical, but by the time the workers started on the seventh floor, the tower was tilting one degree south. Around this time, construction stopped again for unknown reasons. read more