The carved details reveal simplicity of execution, being merely cut back from the surface, the relief being uniform and greatly in contrast to the plastic feeling of the Roman work. Though the leaves employed were of the acanthus type, they were quite devoid of modelling, being merely channelled with V-shaped grooves; the eyes between the lobes being round and suggestive of the use of the drill, the execution being a reversion to the archaic Greek. [Illustration: No. 37. Byzantine Panels. St. Appollinare, Nuovo, Ravenna.] _Early Christian Art_ A notable feature in the Byzantine detail is the prevalence of the circle, frequently grouped in three, four and five, with the respective significance of the Trinity, the Evangelists and the Cross, or Five Wounds. The grotesques of the Pagan detail are conspicuously absent, giving place to forms more in keeping with the new religion, such, for instance, as the cross and the vine. It is questionable if the polytheism of the average cultured Roman was taken very seriously, but incidental to the religious observances were certain rites and symbolic forms, with which the Christians were familiar, and the early preachers evidently found it a matter of policy to invest some of these with a new meaning. During the period of intolerance and persecution, signs and symbols grew in importance as a [Illustration: No. 39. Byzantine Interior, Ravenna.] [Illustration: No. 40. 5th Century Mosaic Work in the Baptistery at Ravenna. From a Drawing by Miss Dora Bard.] means of secret communication; and in the later period when secrecy was no longer necessary, these became a corporate part of the ornament and decoration. [Illustration: No. 38. Byzantine Panel from the sarcophagus of St. Theodore. St. Appollinare in Classe, Ravenna.] In contrast to the Roman ornament, in which the effect depended mostly on light and shade, the Byzantine was a colour style, and it became customary to line the walls of the principal buildings with marble slabs quartered and placed reciprocally, so that the figurings formed symmetrical patterns. Mosaic work, either of marble or glass, constituted the decoration in such suitable positions as the floors, spandrils, lunettes and domes, gold being largely employed in the backgrounds. Windows, at times large in area, were glazed as in Roman times with cast slabs of glass, set in metal frames, usually bronze; and thin slabs of translucent marble and onyx were also used for glazing purposes. _Metal Work and Enamel_ The Byzantines were also expert carvers of ivory and workers in metal, decorated in repoussé and with wire filigree; the metal work was invariably set with jewels and precious stones, in conjunction with champleve enamel, the whole being gilt.