Another disappointing aspect of the present building is the lack of unaltered twelfth century windows. All of the ground-floor windows of the nave have been replaced with larger windows in the Decorated style, and although there are many original twelfth century windows in the transepts and upper levels of the nave they have all been filled with Decorated tracery. Nevertheless the interior of the building provides an impressively unified example of the multitude of great churches that were created in England immediately after the Norman Conquest, although it was in fact the last to be built.
The construction of the Norman building, organised by Norman overlords in church and state, but built by Anglo-Saxon craftsmen, and therefore sometimes referred to as an Anglo-Norman building, lasted about sixty years from about 1107 to 1170. During this period the original plan was altered in several respects. The transepts were originally designed to be as wide from east to west as the choir and nave, with arcades and galleries along both eastern and western sides, but after foundations were laid the western galleries were abandoned, and the transepts made much narrower as they are today, with chapels along their eastern sides. Eventually a single-story vestry was build against the west wall of the south transept in the space left between that wall and the cloister walk.
Another early alteration to the original plan concerned the terminal wall of the south transept and perhaps that of the North transept also. According to Reilly(98) the south wall was increased in thickness to allow for the inclusion of a staircase. This would have been essential to provide access to the roof space, and it may well have been the fire of 1116 that must have mainly developed in the wooden timbers of the roof and probably a ceiling, as happened later at Canterbury, that lead to the decision to set a staircase into this wall. The alteration, probably taking place, according to Reilly, before the construction of the east and west walls of the transept, created problems in the fitting in of their arcades where they meet the terminal walls.
Within the general impression of unity of style pervading the whole of the twelfth century building up to the western transepts, Reilly perceives three minor variations of style. One informs the design of the apse and the chapels of the transepts. The reason for this special treatment of these areas , I would suggest, is that these areas are all sanctuaries, furnished with altars, and therefore especially sacred.
A second stylistic variation is limited to the area of the monastic choir, while the third affects most of the nave, but neither of these have any appreciable affect on the ground-plan of the church.
That ground-plan was however affected by the removal, c.1500, of two small apsidal chapels that stood one either side of the main central apse. They were demolished to provide access to the New Building that was built around the Norman apse to provide an ambulatory processional passage and perhaps, I would suggest, an altar. The history of these choir apses would seem to be uncertain. The subject is referred to in Reilly only in a footnote stating that they “originally ended in apses that were squared off. Although the original terminations have now disappeared, their form was uncovered by Micklethwaite and they are now outlined in the pavement of the south aisle.”
The building we now see was built around a pre-existing Anglo-Saxon abbey church that was much smaller in scale. This was to allow the monastic community to perform the sacred offices of worship that their Rule demanded every day and night of their lives. Thus their ancient chapels and altars continued in use unceasingly until new altars became available and securely housed within the walls of the new church. When this procedure took place at Canterbury in 1096, the architect and organiser, Prior Ernulph, had to build his celebrated new choir, containing at least 22 chapels on three floor levels, around the smaller choir of his predecessor Lanfranc. He therefore had to build it wider. He was then sent as Abbot to Peterborough to build their new monastic church. There he faced a similar task, and laid out the general plan of the church around the old Anglo-Saxon building, but here the presence of the old building would appear to have had no effect on the layout of the new work.