The tower was built in the stages over 199 years, from 1173 – 1372. The tilt began during construction and is caused by an inadequate foundation on ground too soft to support the tower’s weight. It reached an angle of 5.5 degrees but it has now been stabilized at 3.99 degrees after restoration efforts in the late 90s. The cathedral was the first building constructed on the Campo dei Miracoli (Square of Miracles)