What makes the leaning tower of pisa lean?

The leaning tower of pisa northen Italy is a church bell tower. Its constrution began in 1173, but soon was halted when the builders realized the 10-foot foundation wasn't deep enough to keep the tower from tilting in the soft soil. the 180 foottower weighting 1,600 tons, was finaily completed 200 yaers later,. to keep it from topping over, the people from Pisa have repeatedly gone in and reinforce the foundation. But they haven't dared to try straighten the tower!