In the succeeding phase the Triforium which had gradually become less important, entirely disappeared and the clerestory windows enlarged, to the extent that this part of the structure became merely a frame for the increased glass areas.
It will be apparent from the foregoing that whereas in the early churches of the Romanesque period the interior effect was mysterious owing to inadequate openings for light, the later and growing tendency was to increase the lighting capacity by enlarging the windows of the clerestory.
Glass Windows
Doubtless the development in the size of windows was due to some extent to the growing use of glass, which, though rare, was employed during the later Romanesque through Byzantine tradition.
No. 68. Perpendicular Gothic Bay shewing development of Clerestory.
These early windows were geometric in design, consisting of medallions, oval, circular or quatrefoil in shape, containing figure subjects set in a diapered background, the whole being executed in small pieces of coloured glass united by lead framings.
While the windows were single openings, this form of glazing necessarily restricted the size, though more adequate lighting was achieved by grouping two or more windows together.
With the development of tracery the technical difficulties were to some extent overcome; a window divided into comparatively small compartments could be more easily glazed than single openings of large size; thus glazed windows of greater dimensions were rendered possible.