ABSTRACT
By the end of June 1998, underexcavation basically eliminated differential settlements accumulated over the previous 65 years as a result of regional subsidence. When the treatment was completed, the maximum correction induced was 92 cm, between the apse and the southwestern corner. The correction achieved by April 2000 at the west and east towers consisted in rotations and displacements of 28.7 and 27.9 cm, respectively, along a northeast direction. The impossibility of seeing with the naked eye the corrections that were in course prompted the installation of a plumb line at the Cathedral’s central dome in order to make its movements apparent to visitors. The historic pathology of the Tower of Pisa derives from the subsoil characteristics that, as in the case of the Cathedral, evidence non-homogeneous properties. The tower was also underexcavated, having as a precedent the underexcavation of the Mexican cathedral that had begun in 1993.
