In such localities as the North of Italy and Provence, where Roman remains were plentiful, the Romanesque architecture made free use of antique columns and details. But in the Rhine Provinces, the North of France, and England, the lack of such materials and of skilful workmen encouraged the substitution of the pier for the column and caused the latter to be of simpler and in many cases ruder design. Necessity, in fact, compelled the adoption of new forms. Moreover, the desire of the Church to build permanently led to the use of stone in place of inflammable timber, especially in the building of the roofs. Accordingly, the use of vaulting was revived. It was out of the application of these necessities of construction that the Romanesque style was evolved. =Chevêt.=--The basilica plan became gradually modified. The nave and aisles were retained, but the chancel, with or without an apse, was carried farther back and the length of the transepts prolonged, so that in time the cruciform plan prevailed and acquired a symbolic significance. A special feature, gradually introduced, was the _chevêt_ which formed an _ambulatory_ around the sides of the choir and the semi-circle of the apse, and could be divided up into chapels dedicated to individual saints. =Vaulting.=--In the earlier examples the nave was covered with a barrel-vault, the thrust of which was sustained in the first place by strengthening the nave walls by the omission of clerestory windows and, secondly, by the weight of barrel-vaults over the side aisles, their thrust, in turn, being sustained by thickening the outer walls and keeping the windows small. As a further reinforcement of the walls, projecting piers of masonry were built into them, which in time became features of the external decoration. Gradually the barrel-vault was superseded by groin vaults; at first in the aisles and later over the nave as well. The groin vaulting over the aisles represented, as in Roman times, the intersection of two semicircular vaults. But since the nave was usually twice the width of the aisles, each of the nave bays would be oblong in plan. Accordingly two of these were included in one square bay, which took in two of the nave arches and corresponded to two aisle bays. In some instances a shaft was carried up from the intervening pier on each side of the nave, supporting an intermediate transverse arch, so that the vaulting became sexpartite, or divided into six compartments. Whether the bay were six part or four part, the curve of all the groins--longitudinal, transverse, and diagonal--were semicircular. Accordingly, since the diagonals had a longer diameter, their curves rose above the others. This variation was met by giving a concave or domelike surface to each of the compartments, so that the workmen were able to adjust the stones to the differences of the curves.