The roof of the nave was composed of precisely the same parts, only that, being twice as wide as each compartment was broad, the length of the transverse ribs and of the intersecting ogives was greater in proportion to the formerets than in the aisles. Another addition, and certainly an improvement, was the introduction of ridge-ribs (D D), marking the point of the vault. These could not of course be used with circular arches, where there was no centre line for them to mark; and it probably was from this cause that the French seldom adopted them, having been accustomed to vaults not requiring them. Another reason was that all their earlier vaults were more or less domical, or in other words the point C was higher than the points A or B, though this is more apparent in hexapartite vaults, or where one compartment of the nave-vaults takes in two of the aisles, than in quadripartite, like those now under consideration. Still all French vaults have this peculiarity more or less, and consequently the longitudinal ridge-rib, where used, has an up and down broken appearance, which is extremely disagreeable, and must in a great measure have prevented its adoption. There is, however, at least one exception to this rule in France, in the abbey church of Souvigny, represented in the Woodcut No. 661, where this rib is used with so pleasing an effect that one is surprised it was not in more general favour. [Illustration: 661. Abbey Church, Souvigny. (From ‘L’Ancien Bourbonnais.’)] These are the only features usually employed by French architects: but we do sometimes find tiercerons, or secondary ogives, used to strengthen as well as to ornament the plain faces of the vaults, one or two on each face, as at E E (in Woodcut No. 660); small ribs or _liernes_, F F, from _lier_, to bind, were also occasionally used to connect all these at the centre, where they formed star patterns, and other complicated but beautiful ornaments of the vault. These last, however, are rare and exceptional in French vaulting, though they were treated by the English architects with such success that we wonder they were not more generally adopted in France. The most probable explanation appears to be that the French architects depended more on colour than on relief for the effect of their vaults, while in England colour was sparingly used, its place being supplied by constructive carving. Whatever may have been the comparative merits of the two methods when first used, the English vaults have a great advantage now, inasmuch as the carving remains, while the paintings of the others have perished, and we have no means left of judging of their original effect.