| A triforium stands above the transept and the east side, which, on the exterior have six defensive round towers as buttresses. |
| On the south side the westernmost Perpendicular bay, up to the triforium, is solid and covered with cinquefoil panelling. |
| By the end of the 13th century the triforium was usually replaced by greatly heightened clerestory windows. |
| A vast white room, it was, with a wide, white triforium lined with white canvas mattresses. |
| The triforium zone of the basilica features a cycle of over thirty frescoes of the life and legend of Peter, executed in about 1300 and credited to Deodato Orlandi. |
| There are also some in the south-east chapel of the triforium of the choir. |
