The tall Tower of Santa Maria stands on the north-western corner of the medieval ramparts. It is built of tuffaceous stone, and its upper part, resulting from modern remodelling, is pierced by rectangular archivaulted openings.
Construction of the ramparts began in 1155, under the consulate of Cocco Griffi. The first stretch of wall to be completed was between the Torre del Leone and the Torre di Santa Maria, which at the time surmounted the bridge over the River Auser. These two towers, along with the Torre di Santo Stefano and the Torre dell'Arno, are the oldest. The Torre di Santa Maria is closely connected with the structure of the ramparts in that the same tuffaceous material was also used for the tower walls.
The Commune of Pisa decided to begin fortifying the city from the west side because of the importance and vulnerability of the area. In this area were the main religious buildings, whose construction had almost been completed, and the road that connected Pisa to the important French markets. The road entered the city through the Porta del Leone and, passing behind the apse of the cathedral, joined the Via Santa Maria. Both the highway and the River Auser needed to be protected against possible military attacks by Pisa''s enemies. To this end the Pisans erected the Torre del Leone, controlling the bridge of the same name, and the Torre di Santa Maria, guarding the river. The tower by the Auser fulfilled its strategic function throughout the Middle Ages.
In 1499, at the time of the terrible siege by Florence, the two defensive towers were cut down to the height of the ramparts. The additional portion that is visible today was probably added in the latter half of the 19th century with a view to restoring the Torre di Santa Maria to its original appearance.