Toward the second half of the twelfth century the system was still further improved by the introduction of pointed arches and vaults in both nave and aisles, as for example in the abbey church of Cunault (Maine-et-Loire). The flattened type of groin has here been abandoned, though the vaults are not of domed-up type. Such doming is to be found in Poitou, however, in Saint Pierre at Chauvigny (Vienne),[65] probably with the intention of saving centering, as in Byzantine architecture. But even though the builders of Poitou made some progress in vaulting, they never attempted to solve the associated problem of getting direct light in the nave. Hence such progress was but slight from the earliest to the latest churches of the school.[66] THE SCHOOL OF AUVERGNE THE ORIGIN AND USE OF THE TRIFORIUM GALLERY IN AUVERGNE One of the distinguishing features of the typical churches of Auvergne is the presence of a second story or triforium gallery above the side aisles. To account for its presence a number of theories have been advanced. That such galleries were not intended for congregational purposes, at least in the early churches of the school, is evident from the fact that they are but dimly lighted and accessible only by narrow staircases in dark corners. They may have been used for storerooms or treasuries for relics brought by pilgrims,--a possibility which is strengthened by the fact that they ceased to be built in the thirteenth century when the era of the Crusades was past,[67]--or they may have been useful places from which to defend the church, corresponding in this respect to the room frequently found in the second story of Romanesque towers.[68] But whatever their use, they would seem, in Auvergne, at least, to have originated on purely structural grounds. The expedient of dividing the openings from the nave of the church to the aisles into two stages, with the evident intention of thus reducing the height of the piers and even of making lighter piers possible, was employed in a number of churches both earlier and later than those in Auvergne. It may even be in part the explanation of the double colonnade in the Lateran Baptistery, and the upper stories in the chapel at Aachen, and the abbey churches at Essen, Nymwegen, and elsewhere. In any case, it explains the system of two stories of arches in the Carolingian church of Saint Michael at Fulda (818-822),[69] and in the early Romanesque churches of Vignory (Haute-Marne)[70] (eleventh century), Montiérender, (Haute-Marne)[71] (early eleventh century), and Chatel-Montagne (Allier)[72] (early twelfth century), and probably also in Saint Pierre at Jumièges (Seine-Inférieure)[73] (cir. 940).[74]