The city of Pisa is world famous for its leaning tower.
The tower was constructed as a bell tower for the Pisa cathedral.As a memorial of their victory over Saraceans,
the people of Pisa started construction of this tower, which soon ran into problems, when it was noted that the
ground where the towe was being constructed was improper, with soft soil. The building was abandoned after 3 stories
were built.
After a century, one more architect, Giovanni di Simone, started the constuction and changed the axis to stop it tilting
further. It didn't help. However he constructed 3 floors before stopping again.
Since the last few centuries, the tower has stopped tilting. But nobody knows when it may start tilting again. As a
safety measure, it's closed for tourists.
Nobody knows whether the construction of this tower on the soft soil was intentional or an error of judgement, but
they did succeed in making it a world class monument.