And at that point, and that instant, reaching the place that was nearest heaven, the builders looked back, for the last time, to the way by which they had come, and the scenes through which their early course had passed. They turned away from them and their morning light, and descended towards a new horizon, for a time in the warmth of western sun, but plunging with every forward step into more cold and melancholy shade. XXIII. The change of which I speak, is inexpressible in few words, but one more important, more radically influential, could not be. It was the substitution of the _line_ for the _mass_, as the element of decoration. We have seen the mode in which the openings or penetration of the window expanded, until what were, at first, awkward forms of intermediate stone, became delicate lines of tracery: and I have been careful in pointing out the peculiar attention bestowed on the proportion and decoration of the mouldings of the window at Rouen, in Plate X., as compared with earlier mouldings, because that beauty and care are singularly significant. They mark that the traceries had _caught the eye_ of the architect. Up to that time, up to the very last instant in which the reduction and thinning of the intervening stone was consummated, his eye had been on the openings only, on the stars of light. He did not care about the stone, a rude border of moulding was all he needed, it was the penetrating shape which he was watching. But when that shape had received its last possible expansion, and when the stone-work became an arrangement of graceful and parallel lines, that arrangement, like some form in a picture, unseen and accidentally developed, struck suddenly, inevitably, on the sight. It had literally not been seen before. It flashed out in an instant as an independent form. It became a feature of the work. The architect took it under his care, thought over it, and distributed its members as we see. Now, the great pause was at the moment when the space and the dividing stone-work were both equally considered. It did not last fifty years. The forms of the tracery were seized with a childish delight in the novel source of beauty; and the intervening space was cast aside, as an element of decoration, for ever. I have confined myself, in following this change, to the window, as the feature in which it is clearest. But the transition is the same in every member of architecture; and its importance can hardly be understood, unless we take the pains to trace it in the universality, of which illustrations, irrelevant to our present purpose, will be found in the third Chapter. I pursue here the question of truth, relating to the treatment of the mouldings.