The arrival at St. Gregory's in 1133 of a prior and twelve canon's from Merton Priory appears to have provided the impetus for a major programme of rebuilding and modification. A choir was now required for the canon's in the church, and in order to accommodate one, the east wall of the chancel was demolished, the central area of the church enlarged and a new chancel constructed to the east. Additionally, transepts and small, twin-celled side chapels were added to the northern and southern sides of the nave. The side chapels may have formed private shrines, accommodating the relics of the saints.

The structural additions were undertaken late in the life of the Lanfranc church, some perhaps being completed only few years before the fire of 1145, which destroyed the church.

**Previous theories (namely by T. Tatton-Brown) of three earlier late saxon churches on the site side by side, later joined together by a large nave built by Lanfranc are now proven to be incorrect. What were considered to be these three chapels are in fact the extension to the chancel; and the two north and south side chapels that spring off of the transepts, all built onto the original church between 1133 and 1145.

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