When it was built in the eleventh century, the church comprised a nave with three aisles, seven bays long. The central aisle was covered with a barrel vault, the two side aisles with groined vaults (1). The last bay supported a dome, with the church's bell-tower above (2). This nave, without any transepts, ended in a sanctuary surrounded by an ambulatory (3) giving onto three semicircular chapels (4). At the beginning of the twelfth century the church was extended towards the west, with the addition of two new bays (5) and the construction of the magnificent façade it still has today. Towards 1521, a seneschal of Poitiers had a new chapel built to the north-east of the choir (6). This example was followed throughout the fifteenth and sixteenth centuries by various important personages of the city, who added new chapels around the sanctuary and all long the left aisle.