The overall disposition is the same as the nave: indeed, it is likely that Thomas de Cormont, who completed the upper nave, was responsible for the lower choir. However, in the upper choir we see the new type of triforium devised by young Renaud de Cormont. The triforium is glazed, as we have already seen in the eastern side of the transept. But here, in the choir, the triforium bays are capped by a gable, bringing the composition into line with "minor art" manifestations like ivories, metalwork and manuscript illustrations. The clerestory windows feature triple units and trefoils. The exterior flying buttresses, invisible here, have openwork tracery panels. The work has a mechanical repetitiveness. Georges Durand, the greatest historian of the cathedral, remarked, "C'est presque le commencement de la décadence."
It is interesting to note that in the triforium of the hemicycle Master Renaud de Cormont has returned to the basic motif, dominant in his father's work, of the great trefoil.
Note: the three images at the bottom of the page show fire (1258) damage in the triforium at the south-west end of the choir.