The Cathedral Place is enclosed to the west and north by the medieval city walls framing the lawn that highlights the whiteness of the Romanesque monuments: in this part of the wall there are gates and towers, both original andinserted later.
Beginning from the west, these are: Porta Nuova (New Gate) also known as Porta S. Maria, opened in the medieval walls in 1562, the Catallo Tower and door, the Porta del Leone (Lion) door and Tower, with a stone lion standing guard, the S. Maria Tower, that stood by the bridge over the river Auser, a branch of the River Serchio that flowed outside the walls, and at the end of the Place and the St. Stephen tower.
The north-western portion of the walls was built in three stages: the first is the segment between the Torre del Leone and the Torre di S. Maria (1st lot, in 1154), then the northern part was built, between Torre S. Maria and Torre di S. Stefano (4th lot in 1156), finally the western stretch, between the Torre del Leone towards the Spedale di Santa Maria (5th lot in 1157) in which the S. Maria gate was later opened.
The oldest lot was built from large blocks of yellow panchina stone, quarried on the coast of Livorno. This suggests there may have been a previous wall, either Etruscan or Roman. The remaining walls are built in stone from different quarries: the lower zone, in grey stone, is in limestone blocks from quarries at San Giuliano, the pinkish one above it is in squared blocks of breccia from quarries at Asciano, both at the foot of the Monte Pisano.