_Decoration._--Of the churches of Constantinople only S. Sophia, S. Mary Diaconissa, the South Church of the Pantokrator, and the Chora, retain any considerable part of their original decoration. The first is beyond our present scope, but from the general tone and atmosphere which still linger there we are able to appreciate the effect of the same style of decoration where it survives in less complete form. The accepted method, as may be observed in the Chora and the Diaconissa, was to split marble slabs so as to form patterns in the veining, and then to place them upright on the wall. It is probable that the finest slabs were first placed in the centre points of the wall, and that other slabs or borders were then arranged round them. The centre slabs in the Chora are of exceptional beauty. The usual design consists of a dado of upright slabs surmounted by panelling to the cornice level, the panels being outlined with plain or carved beads. In the Diaconissa the notched dentil form is used for the beads; in the Chora, a 'bead and reel.' The arches have radiating voussoirs, or, in the Diaconissa, a zigzag embattled design, found also in S. Demetrius of Salonica, though two hundred years must have separated the buildings. In the Chora the arch spandrils and cornice are inlaid with scroll and geometrical designs in black, white, and coloured marbles. The surfaces above the cornice and the interior of the domes gleamed with mosaic, representing, as seen in the Chora, figures on a gold background. The mosaic cubes are small, measuring 5 mm. to 7 mm., and are closely set. This is about the same size as the mosaic cubes in S. Sophia, but smaller than those at Ravenna, which measure about 10 mm. _Painting._--In the majority of churches this full decoration with marble and mosaic must have been rendered impossible by the expense, and accordingly we find examples like the parecclesion at the Chora decorated with painting, following exactly the tradition of marble and mosaic. This painting is in tempera on the plaster, and is executed with a free and bold touch. _Conclusion._--Byzantine architecture is essentially an art of spaces. 'Architectural' forms, as we are accustomed to think of them, are noticeably absent, but as compensation, colour was an essential and inseparable part of the architecture. The builder provided great uninterrupted spaces broken only by such lines and features as were structurally necessary--capitals, columns, string-courses, and over these spaces the artist spread a glittering robe of marble or mosaic. No school has ever expressed its structure more simply, or given fuller scope to the artist, whether architect or painter.