PISA the hanging tower; bell tower of the Dome. Postcard 1955 approximately. The tower was constructed beginning from 1173 approximately. The attribution of the plan is discussed; and the names of the possibilie partenit?are Diotisalvi; author also of the baptistry; Gherardo di Gherardo; or; according to the Vasari; Bonanno Pisano. The cedevolezza of the land; due to the presence of waterbearing stratums; is the cause of the slope of the tower. the intense activities treminarono of the 14th century under the guide of Giovanni di Simone and Giovanni Pisano