[215] The other three are, the sexpartite and pseudo-sexpartite vaults and the irregular four-part method employed at Durham.
[216] Moore, p. 80, Fig. 32.
[217] Whether these concealed buttresses were first used in Normandy or the Ile-de-France is an open question, but in either case their origin would seem to be traceable to such prototypes as the ramping walls above the transverse aisle arches of such Lombard churches as Sant’ Ambrogio at Milan and perhaps even to Roman monuments like the basilica of Maxentius at Rome. The really important question is to learn when these concealed buttresses were first raised above the aisle roofs to constitute true flying-buttresses. This would seem to have taken place in the Ile-de-France, perhaps at Domont as Porter suggests (Porter, II, pp. 91-92), or at Noyon towards the middle of the twelfth century.
[218] Ill. in Moore, p. 76.
[219] An example of the heavy ribs used in early work may be seen at Morienval, Fig. 77.
[220] These and the following churches are chosen at random merely for the purposes of comparison.
[221] For example in the cathedral of Albi, where the nave is sixty feet in width, and in that of Gerona (Spain), where it is over seventy.
[222] See pp. 49 and 70.
[223] See Bond, p. 336.
[224] See Bond, p. 335.