THE MEDIEVAL CATHEDRALS 425 and ornamentation is characteristic of the Gothic. Pointed vaults and arches permit almost endless variety, since height and width do not have to be in any fixed ratio. And they are stronger structurally, since they do not tend to spread Dutward as much as the Roman arch. By coming to a point at the top, they lead the eye upward and were especially adapted to the lofty effects which the architects were striv- ing to obtain. A solid buttress rests on the ground and is built directly |nto or against the wall of a building at points where addi- tional thickness and strength are necessary. We The flying niave seen that the outer walls of the side aisles buttress were often so braced in Romanesque buildings. But the loftier and heavier walls of the nave above the roofs of the jiisles could not be so braced. Here the flying buttress came n. Touching the wall of the nave only at one end, it sprang dear of the roof of the aisle in an arc of stone whose other xtremity rested on one of the solid buttresses that rose from the ground to meet it. Thus no new weight was put upon he roof of the aisle, and the buttresses of the outer walls £ the aisles were made to bear the burden of the nave wall is well. Of course, to do this, they had to be made thicker. The flying buttresses, moreover, not merely propped up the ide walls of the nave, but were placed at the proper points b receive the thrust of the heavy vaulted roof. Of course, pme of the weight of the nave walls and roof still rested on tie rows of columns within the church, but these did not eed to be as massive as before. As a matter of fact they ^mained nearly as great in actual diameter as before, but . rere made higher and were placed at greater intervals apart, llso the square piers and huge round pillars were replaced y more graceful clusters of slender columns, which hid the antral core of masonry that united and strengthened them, nd from which as they rose diverged the supporting ribs f the arched vaulting overhead. Since these ribs, columns, tid flying buttresses supported the whole burden of the aulting, it was no longer necessary to have thick or solid 'alls in the nave, and the clear-story could be given over
