Why tower of Pisa is so popular ? Because the story behind the construction of the tower. The tower was designed to be bell tower for Pisa Cathedral. They start the construction August  1173 , but when it reached the construction of the third floor,start tilting or leaning ,because the foundation is so soft.and they stop the construction, then there is war is going on and forget the construction for ninety years and the foundation get more stabilized ,firmed.and on the half of the 14th century they completed the construction.and the whole construction took almost three hundred years. And the tower still gradually leaning every year . Until they spend millions of dollars to restored it. And today the tower is restored. And the whole world love it.Below is the PISA CATHEDRAL