In its original form, traditionally dating to 1084, Lanfranc's church of St. Gregory had the simple plan of a long, aisleless nave and a small, rectangular chancel to the east. The nave was c. 16.60m long and had a maximum width of c. 6.70m; the chancel was c. 3.50m long and 5.30m wide. The chancel floor was raised above the level of the nave by c. 0.25m, access into the chancel from the nave would probably been via an archway. The main entrance into the church may have been located at the west end, whilst a doorway was perhaps positioned in the south wall of the nave to provide access into the cemetery.

Tradition records that six priests and twelve clerks formed the community at St. Gregory's, living under a rule, caring for the sick of St. John's hospital, baptising, burying and hearing confessions. These individuals must therefore have lived at the site of St. Gregory's, presumably in accommodation adjacent to, and probably north of , the church, since the cemetery was located to the south. In 1133 a prior and 12 canon's arrived at St. Gregory's and a programme of rebuilding was undertaken. Part of this work involved changes to the church. A choir was created for the canon's by building a new chancel as an extension at the east end and the former chancel was converted into a choir; also transepts were added either side of the east end of the nave at the choir junction and a twin-celled chapel was added to each of the transept arms. The work had only just been completed when in 1145 the whole church and other structures were destroyed by a serious fire.

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