It is quite certain from Procopius and the poem of the Silentiary that the vaults of Justinian’s church were covered with mosaic. They both describe the brilliance of the gold glittering surface, but do not mention any figures. In such detailed descriptions this silence goes far to show that there was originally no storied scheme of imagery, like that which the Poet so fully traced out on the curtains and iconostasis. It seems equally certain that where, describing the dome on the strong arches, overhanging the interior like the firmament which rests on air, he says, “at the highest point was depicted (_epigraphe_) the cross, Protector of the City,” we are to understand that a great cross in mosaic expanded its arms on the zenith of the dome, and that the background was strewn with stars. Now this is a well-known scheme, and it is found at an earlier date in the chapel of Galla Placidia at Ravenna, and later it is mentioned by Porphyrogenitus in a description of a domed apartment in the palace. The stars on the dome are more than once referred to in the poem (page 36), and it is probable that the surfaces between the ribs as well as the central circle had gold stars set in azure, the ribs being of gold; nothing less would seem to justify “the firmament of the roof its rounded expanse sprinkled with the stars of heaven.” It is evident that, however easily figures and pictures might be added here and there at various dates, the church, being once incrusted with mosaic, would at no subsequent time have had the enormous areas of tesserae removed to be again renewed. It follows that the ground, and any patterns evenly distributed in every part of the vaults, are assuredly of the first work. First among such designs is a jewelled cross thirteen feet high, which is blazoned on both ground floor and gallery vaults, and which must have been repeated some twelve times twelve. We give an outline of one of the smallest vault compartments in the church, the irregular space to the east directly south of the bema: here three of the crosses can still be seen through Fossati’s colouring, their interlocking arms spreading over the whole field. This form of cross, with lobed ends, is found set in a circle of stars, in the mosaic apsoid of S. Apollinaris in Classe. (Fig. 70.)