During a major programme of rebuilding after a prior and twelve canon's arrived at St. Gregory's in 1133, changes were made to Lanfranc's original church building. The east end was extended to give a new chancel, the former chancel being converted into a choir for the canon's, north and south transepts were added either side of the nave both having side chapels, perhaps shrines to allow accommodation of relics of the saints. The work was carried out between 1133 and 1145 and was probaly only just completed when the church was burnt down in a serious fire in 1145.

The new south transept was roughly square in plan measuring c. 5.30m wide N-S by c. 5.70m long E-W. It was sited so that its east wall was in alignment with the nave/choir dividing wall, and both east and west walls butted to the earlier nave wall.. It probably connected to the nave via an archway, and perhaps an arched way through into the side chapel. The side chapel was twin-celled ; both cells were rectangular shaped in plan the western measured c. 3.90m long E-W and c. 3.20 -3.40 m wide; the smaller east cell was c. 2.30m long and 2.50m wide.

The northern transept and side chapel was almost a mirror image of the southern although the measurments varied slightly. The transept was roughly square ion plan weasuring c. 5.40m long E-W by c. 5.35m wide N-S. The side chapel was twin-celled the larger west cell measuring c. 3.80m long E-W and c. 2.95m wide N-S.

Hicks, A. & Hicks, M., 2001, St. Gregory's Priory, Northgate, Canterbury, Excavations 1988-1991 (Monograph). SKE30367.