It must be borne in mind that the great constructive and reconstructive movement which had manifested itself throughout Western Europe, and notably in the north of France, by great buildings, the distinguishing characteristics of which are vaulted roofs and flying buttresses, had made little progress in Southern France. The few exceptions of importance are--Bazas, Bayonne, Auch, Toulouse, and Narbonne. The Southern architects, as we have already stated, adhered to the ancient tradition, whether influenced by impulses of reaction, resistance, or defiance. Their conservatism is comprehensible enough in view of the strong Gallo-Roman tendencies which governed architectural activity throughout the district. The builders of the thirteenth and fourteenth centuries did indeed accept the Angevin intersecting arch, an invention the admirable simplicity of which was its own recommendation. But this concession was without prejudice to their broad principles. In the general arrangement of their religious buildings they still adhered to Roman usage, and to such models as the Basilica of Constantine and the tepidarium of the Baths of Caracalla.[20] [20] _L'Architecture Romane_, by Ed. Corroyer; Paris, Maison Quantin, chaps. iii. and vii. Towards the close of the thirteenth, and throughout the fourteenth century, a large number of churches were built in the South, consisting of a single wide and lofty aisle, vaulted on intersecting arches, the thrusts of which were received by buttresses of great bulk and prominence in the interior of the building, but very slightly indicated on the exterior. The spaces between the massive interior buttresses, on either side of the aisle, were occupied by a series of chapels, supporting disconnected tribunes or a continuous corridor. The two great churches of the Cordeliers and of the Jacobins at Toulouse were built in the brick of the country in the second half of the thirteenth century. These have two aisles, according to the Dominican usage of the period, but the exterior arrangement is the same as in the one-aisled churches. The Churches of St. Bertrand at Comminges, and those of Lodève, Perpignan, Condom, Carcassonne, Gaillac, Montpezat, Moissac, etc., were built in the fourteenth and fifteenth centuries on the single-aisled plan. That of Perpignan has this peculiarity; its vaults, though supported on intersecting arches, are built in accordance with Roman methods, which further prevail both in the forms of the terra-cotta materials, and in the manner of their application. The reins of the vault, which measures some 53 feet across, are ornamented by terra-cotta jars embedded in an admirably prepared lime mortar of great durability. The actual roof lies without the support of any intervening structure of timber upon the extrados of the vault. This consists of voussoirs of Roman brick, retained by a layer of terra-cotta upon which the tiles, also of the antique Roman form, are laid.