Byzantine architecture, seen especially in the churches, became a leading form of art. Its most striking feature is the dome, which replaces the flat, wooden roof used in the basilican Churches of Italy. The exterior of a Byzantine church is plain and unimposing, but the interior is adorned on a magnificent scale. The eyes of the worshiper are dazzled by the walls faced with marble slabs of variegated colors, by the columns of polished marble, jasper, and porphyry, and by the brilliant mosaic pictures of gilded glass. The entire impression is one of richness and splendor.