pierced trefoil in the tympanum above. But already a new and far-reaching development of these germ forms had begun whose progress was most rapid. In the clerestory openings of St. Leu we have coupled pointed arches surmounted by a circle, within which is a thinner plane of masonry pierced with a six-foiled opening. Internally the longitudinal rib forms an encompassing pointed arch to the group, and externally there is a similar arch in the wall which projects beyond the plane of the grouped openings, throwing the design into two orders, as in Fig. 47. Windows like these of St Leu, though more enriched in having moulded archivolts and shafted jambs, occur also in the clerestory of the choir of Soissons. In these examples we have the radical forms of a great variety of subsequent Gothic apertures.
As I have before remarked, constructive development was the moving cause of change in every portion of the building, and the enlargement of the apertures was rather due to the nature of the construction than a result of endeavour to produce a beautiful and imposing effect, though such endeavour doubtless became also operative as constructive development went on.
The apertures of the clerestories of St. Leu and of Soissons were followed almost immediately by those of the apsidal chapels of the Cathedral of Reims, which date from about 1215, and though designed on the same general scheme, present an entirely new character (Fig. 48). For here, instead of solid spandrels between the main openings, we have lesser openings following the outlines of the larger ones; and thus instead of grouped openings we have rather a single opening divided by slender bars of stone. Moreover, these bars are no longer left, like the former pierced masonry, with plain flat surfaces, but are lightened and enriched by mouldings which, on the jambs and on the mullion, assume the forms of slender shafts with capitals and bases. In short, what may be called the pierced plane of masonry of St. Leu is here converted into Gothic tracery.
The great change referred to above, which was wrought soon after its first completion in the clerestory of Paris, consisted chiefly in substituting for the old ones openings like those of the apsidal chapels of Reims. But these new openings of Paris mark one further step in the development of tracery.
