Why doesn't the leaning tower of Pisa fall over?

The eight storied tower of white marble is tilted 16 ft. To one side. It has tipped one foot during the past 100 years, and some engineers call it the falling tower of Pisa, because, without a doubt, it will someday topple to the ground. However, it has stood safely since the year 1350 when it was finished. The famous building was started in the year 1174, and it was soon plain that all was not well. The weighty marble was too heavy for its sandy foundations, but the builders did not give up their plans. They merely changed the construction weight of the unfinished stories to overcome the faulty foundation and hoped for the best.  more

I went to the tower in April and went up. Behind the tower (from the popular view) is what looks to be some huge hydraulic pumps. My guess is that even though the tower is stable now and people can go up it, the mechanism is in place to correct if it ever starts to move again.  more