The northern flank has most of the external decorations, including a rich portal with a sculpted architrave depicting the Last Supper, signed and dated (1166) by the master Gruamonte.
[3] During the last medieval enlargement, the church received its current plan with a single hall and a rectangular apse, incorporating the former northern wing of the cloister.
The small columns are in stone, decorated with capitals featuring heads of lions and oxen, while the arches and the walls are in brickwork.
Left of the entrance, on the northern wall, is a white ceramic glaze depicting the "Visitation", by Luca della Robbia.
On the southern walls is the ambon, sculpted by Fra Guglielmo da Pisa, but also thought to have been a collaboration completed along with Arnolfo di Cambio.
The high-relief sculptures, in Apuan marble are engraved with "Realizzato nel 1270," originally had a polychrome glass background, now mostly lost.