Construction of the third perimeter wall began in 1155. The dates mentioned by Maragone in his Annales are unclear. In some areas the fortifications joined pre-existing defences, taking advantage of a hydrographic situation which already provided natural defences (the River Auser). The urbanized areas around the new wall had already been provided with the necessary external defences, even if these systems did not include real ramparts. Construction began in 1155 in the area corresponding to the present-day Field of Miracles.
The site was not chosen at random, since the ramparts were meant to protect the cathedral and future baptistery and to defend the most vulnerable point in military terms, i.e. the bridge on the Auser to the north-west of the city. Other parts of Pisa were protected by natural barriers such as the Auser itself and the marshes surrounding the city. In this area the wall is different in terms of both design and materials. A vertical construction method was adopted instead of using a longitudinal pattern involving the superimposition of horizontal layers.The stone used was ''panchina'', a sort of tufa stone. There is no continuity between the structure of the wall and that of the towers. The second lot was started in 1156 with the construction of wooden defences around the Civitas and the district of Kinzica for fear of Frederick Barbarossa.
The third lot was begun in the same year with the building of the stretch of wall between the San Zeno area and the Porta Calcesana. Canals were dug from the Monte Pisano to San Zeno for the barges that were to transport the stones needed to build the wall. Greyish limestone from San Giuliano was used instead of panchina. The wall was erected to a height of three ''ponti'' (the ''pons'' was the conventional unit of the time) plus one ''ponte'' for the foundations. The foundations and the lower layers are built of choice material, whereas the upper layers are homogeneous.
The fourth lot was started in 1157-58 with the construction of the section that skirted the Auser, rising to a total height of three ponti, one for the foundations plus two in elevation. The new section ran from the Ponte Santa Maria to the Ponte di Santo Stefano, and from the Porta del Parlascio, the new hub of city life, to the Porta San Zeno.
The fifth lot was started in 1158 with the construction of three ponti of wall, one for the foundations and two in elevation. The new stretch of wall extended from the Porta di Spina Alba to the Porta Calcesana, from the Porta del Parlascio to the Ponte di Santo Stefano and from the Torre del Leone to the Hospital of Santa Maria.
The sixth lot was started in 1159 on the west side of the Via Santa Maria. The seventh lot, begun in 1161, connected the west side of the city, from the Portello to the Torre dell''Arno. The material used was a pink-grey stone quarried at Asciano.