Fig. 34.—Albi, Cathedral.
The use of rectangular four-part ribbed vaulting was not confined to churches with side aisles, but appears also in those with a single broad nave. It is the method employed in the Sainte Chapelle at Paris (fin. 1248), where there are simple salient buttresses, and there is a splendid example in the Cathedral of Albi (Tarn) (begun 1282) [(Fig. 34)], where the nave has a very wide span and is flanked by chapels in two stories between heavy pier buttresses which are thus enclosed in the church in a truly Byzantine manner. In the smaller church of Saint Nicholas at Toulouse these buttress chapels are in but one story and the bays are more nearly square in plan, a compromise between the square and rectangular systems which appears on an even larger scale in the cathedral of Saint Bertrand-des-Comminges (Haute-Garonne) (cir. 1304). As far as construction is concerned these vaults over a single broad nave offer no advance over those in churches with side aisles, not even requiring a scientific system of flying buttresses to offset their outward thrust. Their only importance lies in the very broad space sometimes covered by them.[221]
Vaulting with Added Ribs
The simple forms of ribbed vaulting just discussed were the ones most frequently in use during the best Gothic period. But among certain builders, there was a tendency even in the thirteenth century to introduce additional ribs into the vaults, a custom which later gave rise to a vast number of complicated vaulting systems especially in England, Spain and Germany. Even to enumerate these would be almost impossible and a description of each is out of the question, hence only those combinations which were frequently employed, or which gave rise to new types, will be discussed.
Origin and Use of the Ridge Rib
Naturally enough the ridge rib was the first to be added to those already constituting the four-part vault ([Plate I-j.]). But the vaults thus formed should be divided into two groups. The first most frequently found in France and already discussed in connection with the churches of Anjou,[222] is that in which the surface of each severy has a curved crown and the rib follows this curve, with the object, probably, both of subdividing the large rectangular bays, of marking with absolute exactness the crown line, and of aiding in rigidly fixing the central keystone, or even in the case of a six-part vault, of giving the same apparent division to the transverse severies as is found in those running longitudinally.
Though very similar to this first type, the second, which was developed and most used in England, is different, in that the ridge line is here