It was almost falling, but it was repaired. According to science, anything will remain stable as long as the vertical line drawn from the centre of gravity passes through it base. The centre of gravity is that point where the whole mass of the body is supposed to be concentrated. Till today the vertical line from the centre of gravity has bee falling within the base of this tower. That is why it has not fallen. It is believed that when the tower leans further and the line from its centre of gravity passes out of its base, it will fall down.