South choir aisles, dado and aisle windows
This view provides an excellent indication of the spatial regime of the nave aisles before the addition of the lateral chapels. Here in the choir the dado with its trilobed arches is of exactly the same kind as that found in the transept and in the nave (the latter known only from fragmentary surviving elements). It is thus probable that the first master mason, Robert of Luzarches, laid out the entire cathedral down to the eastern termination of the choir aisles in the 1220s. His successor, Thomas of Cormont, did the choir aisle windows in the 1230s.