Fourth Phase c.1240-50: Thomas de Cormont
The upper nave was finished in the 1240s as attested by the remarkable homogeneity of the work and a 1243 text recording the presence of bells in the south west tower (turre versus claustrum). The western façade was finished up to the cornice over the rose, but the details of the triforium and kings’ gallery had not yet been inserted. In the choir the aisle walls of the straight bays had already been brought up to the window sills; Thomas now continued these outer walls up to the aisle vaults; laid out the hemicycle, ambulatory and radiating chapels (different kind of dado) and built the main arcade up to the triforium sill. Choir aisles, ambulatory and chapels were vaulted.