The floors were paved with richly coloured marbles, in _opus sectile_ or _opus Alexandrinum_. Marble, also, cut in thin veneers and arranged so that their veining produced symmetrical designs, was applied to the walls. Marble, again, but incised with carved ornament, covered the soffits of the arches, the archivolts, and spandrels, while the vaulting was resplendent with mosaics, composed of figures and ornaments, executed in enamelled glass upon a background of gold or blue or, more rarely, pale green. Colour was pre-eminently the motive of the interior decoration and to this end carved work was subordinated. The ornament was in very low relief, spreading over the surface in intricate patterns, that suggest the delicate enrichment of lace. Mouldings were replaced by bands of mosaic or marble, carved or smooth. The chief motive of the carved ornamentation was the mingling of the acanthus and anthemion. The treatment of both was rather Hellenic than Roman; the foliage having pointed ends; but it was deeply channelled and drilled with deep holes at the springing of the leaves. In fact, the use of the drill as well as the chisel was characteristic of Byzantine carving and emphasises the suggestion of the ornament being raised rather than, as in Roman decoration, applied. Corresponding to the general flatness of the ornament is the constraint of the contours of the mouldings, suggestive of Asiatic languor and in marked contrast to the vigorous profiles of classic architecture. The impression, indeed, of the whole scheme of decoration is rather one of soft richness, as carving melts into colour and colour deepens and glows and finally passes into the gold or depths of azure of the vaulting. When the supply of antique columns was exhausted the Byzantine architects began to imitate them, but soon departed from the classic type. In certain cases the capital retained something of its derivation from the Ionic or Corinthian styles; but gradually a new type was evolved, which was distinguished by being convex to the outside rather than concave. The motive appears to have been to give additional support to the arch, for which purpose an _impost_ was, as the name implies, “placed upon” the capital. It consists of a block, which projects beyond the edges of the capital to fit the extra thickness of the wall and may represent, as has been suggested, the survival of a part of the architrave of the discarded entablature. In the decoration of the capitals the foliage was sometimes enclosed in frames of interlace, or the latter took the form of a basket, on which birds are perching. =Pendentive Dome.=--We have now to consider the most characteristic feature of Byzantine architecture--the Dome. Briefly, in the 200 years that divided Justinian from Constantine the Byzantine architects perfected a principle of dome construction by which they crowned a square plan with the circle of a dome.