The measured height is the least interest of a church. The architect's business is to make a small building look large, and his failures are in large buildings which he makes to look small. One chief beauty of the Gothic is to exaggerate height, and one of its most curious qualities is its success in imposing an illusion of size. Without leaving the heart of Paris any one can study this illusion in the two great churches of Notre Dame and Saint-Sulpice; for Saint-Sulpice is as lofty as Notre Dame in vaulting, and larger in its other dimensions, besides being, in its style, a fine building; yet its Roman arches show, as if they were of the eleventh century, why the long, clean, unbroken, refined lines of the Gothic, curving to points, and leading the eye with a sort of compulsion to the culminating point above, should have made an architectural triumph that carried all Europe off its feet with delight. The world had seen nothing to approach it except, perhaps, in the dome of Sancta Sophia in Constantinople; and the discovery came at a moment when Europe was making its most united and desperate struggle to attain the kingdom of Heaven. According to Viollet-le-Duc, Chartres was the final triumph of the experiment on a very great scale, for Chartres has never been altered and never needed to be strengthened. The flying buttresses of Chartres answered their purpose, and if it were not a matter of pure construction it would be worth while to read what Viollet-le- Duc says about them (article, "Arcs-boutants"). The vaulting above is heavy, about fifteen inches thick; the buttressing had also to be heavy; and to lighten it, the architect devised an amusing sort of arcades, applied on his outside buttresses. Throughout the church, everything was solid beyond all later custom, so that architects would have to begin by a study of the crypt which came down from the eleventh century so strongly built that it still carries the church without a crack in its walls; but if we went down into it, we should understand nothing; so we will begin, as we did outside, at the front.