The churches described hitherto possessed simple tunnel-vaults either of round or pointed forms, or, having no side-aisles, were roofed with square intersecting vaults of equal dimensions each way. The former plan was admissible in the bright South, where light was not so much required: but the latter expedient deprived the churches of several things which were always felt to be the powerful requisites of an internal style of architecture. Without the contrast in height between the central and side aisles, the true effect of the dimensions could not be obtained. Without the internal pillars no poetry of proportion was possible, and without an ambulatory, processions lost their meaning. The compartments of the aisles being square, no difficulty was experienced as regards them; but the central aisle being both higher and wider, it became necessary either to ignore every alternate pillar of the aisle, and to divide the central roof equally into squares, or to adopt some compromise. This difficulty was not got over till the pointed arch was introduced; but in the meanwhile it is very instructive to watch the various attempts that were made to obviate it. [Illustration: 614. Fig. 1, after Vaulting; Fig. 2, before Vaulting. Section of Nave of St. Stephen, Caen.] [Illustration: 615. Diagram of Vaulting.] [Illustration: 616. Elevation of Compartment of Nave of St. Stephen, Caen. (From Pugin.)] There can be little doubt that the Norman architects, with true Gothic feeling, always intended that their churches should eventually be vaulted, and prepared them accordingly, though in many instances they were constructed with wooden roofs, or compromises of some sort. Even at Jumièges, the alternate piers were made stronger, and the intention there and in other instances seems to have been to throw a stone arch across the nave so as to break the flat line of the roof, and give it at least a certain amount of permanent character. In the Abbaye-aux-Hommes, Caen, even this does not appear to have been attempted in the first instance. The vaulting shafts were carried right up and made to support wooden trusses, as shown on the right hand of the diagram (Woodcut No. 614).[31] The intention, however, may have been to cut these away when the vault should come to be erected. In England they frequently remain, but rarely, if ever, in Normandy. The next step was to construct a quadripartite vault over the nave, and a simple arch supporting its crown over the intermediate shaft. This was soon seen to be a mistake, and in fact was only a makeshift. In consequence at Caen a compromise was adopted, which the Woodcut No. 616 will explain,—a sort of intermediate vault was introduced springing from the alternate piers.[32] Mechanically it was right, artistically it was painfully wrong. It introduced and declared a number of purely constructive features without artistic arrangement or pleasing lines, and altogether