The respond on the main pier at each end of this arcade is a kind of pilaster strip,[265] surmounted by a capital in low relief, and surrounded by a notched border. The two cornices running round the nave, which serve as galleries for the lamplighters, have an extremely simple profile. The slanting under-surface, divided horizontally by a row of beads, has acanthus-leaves in the upper part forming a cymatium, and in the lower modillions carved with ivy and acanthus, and between them, panels with different leaf-ornaments. Beneath the aisle cornice is a frieze of marble mosaic. The base mouldings or skirtings are worked out of thin slabs.[266] Salzenberg’s Plate xx. contains a collection of architectural details, which seem to belong to different periods; Figs. 1, 2, 3 represent one of the white marble capitals which adorn the two porphyry columns of the south-east porch. The arch above them is Turkish, and hence it may be questioned if this was their original position: they seem more intended for an ornamental structure than to support a load, and they may perhaps have belonged to a ciborium above the holy table. The two marble capitals (Figs. 4 and 5), only three inches thick, were found in the chamber in the north-east buttress mass, above the gynaeceum roof, together with broken pieces from a window. They may originally have belonged to the upper part of the building, such as the window wall under the north arch of the dome.[267] The workmanship is very different from that in the rest of the church, and is more closely allied with ancient treatment. Perhaps they are fragments from the earlier church which found a fresh application in Justinian’s building. The parapet pillars between the twin columns of the western gynaeceum, with tall pedestals, are each formed in one piece of verde antique. Their capitals resemble those of the windows,[268] with the exception that the former are rounded underneath instead of being square. The wood ties which span different arches are adorned on the sides and beneath with carvings.[269] _Windows and Doors._--The lighting of the church is most brilliant; wherever space or construction permitted, windows of considerable size were opened, so that light floods the whole church. At the foot of the dome the light streams in through forty windows, and each of the seven apses has five openings. The eastern sun sends its first rays through the six windows in the apse, and the setting sun shines through the great west lunette. There are twenty-four windows in the two great tympana, besides large windows in the aisles.