The “classical system,” as this close interrelation of architecture and mosaic has been called, was probably perfected in the course of the 9th to 10th centuries, but the earliest fully preserved examples are from the 11th to 12th. Besides Daphni, Greece owns two more monuments of this kind, the monastery church of Hosios Loukas in Phocis and the Nea Moni on Chios (both 11th century). Similar churches are found in such widely distant places as Kiev (Hagia Sophia, 11th century) and Palermo (Martorana, c. 1150), both the products of strong Byzantine influence. The system, however, is not identical in any of these. The churches belong to the same general type, but their plans and elevations vary and thus require variations in this disposition of pictures as well.
The classical system with its emphasis on totality may have led to the gradual toning down of the many splendid effects of the earlier tradition for the sake of the equilibrium and clarity of the whole. At Daphni, for example, the rich, tapestry-like character of earlier mosaic has given way to a controlled, less sparkling range of tints. The reds and yellows are restricted, their function in the overall scheme taken over by the gold of the background. Sombre, often hard blues, greens, and violets are preferred to the lighter ones. Compared with the Hosios Loukas and the Nea Moni mosaics, which retain more of the older colour scheme (the latter almost to the point of brutality), the Daphni mosaics appear cool and intellectual, an impression further conveyed by their elegant style. Actually they belong to a new phase of Byzantine art which took its name from the dynasty of the Comnenus (1081–1185 bce). This style appears at its most refined in Hagia Sophia, Istanbul, in a panel depicting the Virgin flanked by the emperor John Comnenus II and his wife Irene. The practice of tilting the gold tesserae also seems to have been abandoned, for it is not found at Daphni nor in any of the mosaics that are examples of the fully developed classical system. Silver was reduced to the single role of depicting the light emanating from God and Christ. This drying out of the effects of light and colour was partly compensated for by a perfectionist setting and spacing of the tesserae. Late Byzantine mosaics
The phenomenon called the Palaeologian Renaissance (from the dynasty of the Palaeologians, 1261–1453) led to a renewal of Byzantine mosaic art. The stylistic innovations that made themselves felt both in painting and mosaics of the late 13th and beginning 14th century bear witness to one of the most startling changes that ever took place within the framework of Byzantine culture. Bred by a vital humanism, which penetrated westward and laid the foundations for the Italian Renaissance, painting showed a predilection for perspective and three-dimensionalism. A peculiar vivacity invaded religious art, together with a sense of pathos and of the tragic. The results, as expressed in mosaics, were extraordinary.
To respond to the new trend, mosaicists recast their technique. The tessera size generally became smaller than it had been in earlier epochs; and contours lost their rigidity, became thinner, and were occasionally abolished. Colour was reintroduced in a manner that gives the Palaeologian works a striking likeness to the mosaics of the Early Christian period, which, one must suppose, in many cases served the artists as models. An interest in the optical effects of gold apparently returned but rarely, it seems, in the form of the tilting technique. On flat walls, the gold ground was sometimes set in a shell pattern, probably to enhance the play of light on the surface and to avoid a too-uniform brilliance. For domes, a densely ribbed form of cupola construction, which, when covered with mosaics, produces reflections of light that expand like rays from the central medallion toward the figures surrounding it, was preferred. Such domes are preserved in Kariye Cami, the former church of the Chora, at Istanbul, which was reconstructed and decorated as an act of piety by the logothete, or controller, Theodore Metochites in the second decade of the 14th century. Another superb example is found in Fetiye Cami (Church of the Virgin Pammakaristos) in the same city.
The feeling for colour, which is at its most refined in fragments from the decoration of the Church of the Holy Apostles in Thessaloníki (c. 1315) and at its most intense in the partly well-preserved cycles in the Kariye Cami, informs one of the greatest mosaic works of art, the Deësis panel in the south gallery of Hagia Sophia in Istanbul. In this same panel, the tilting technique reappears (in the cross arms of Christ’s halo)—another indication of the retrospection inherent in late Byzantine art.
No mosaic in the true Palaeologian style has survived outside Byzantium. Reflections of it are found, however, in some of the 13th- and 14th-century works at Venice and in the mosaics executed by Pietro Cavallini in the apse of Santa Maria in Trastevere in Rome (c. 1290–1300). Some of the characteristics of the style may have been brought to the attention of the Italian artists through portable mosaics, which despite their small size (generally about 2 by 4 to 8 by 10 inches [5 by 10 to 20 by 25 cm]) are imbued with many of the coloristic and technical features typical of monumental mosaics. Byzantine mosaic icons, the production of which was stimulated during the early Palaeologian era, were manufactured for personal devotion more than for the embellishment of churches and were exported in considerable numbers to the West or found their way there as gifts or booty in the politically troubled 14th and 15th centuries. In works whose quality can be compared with the most splendid of the Hellenistic emblēmata, extremely small tesserae, some measuring less than 0.04 inch (1 mm) square, were assembled in wax or mastic on a board of fine wood. The tesserae material is often exquisite: silver, gold, and lapis lazuli and other semiprecious stones. The icons depict single figures such as saints, Christ, or the Virgin; single Christian scenes such as the Annunciation (Victoria and Albert Museum, London) and the Crucifixion (Staatliche Museen zu Berlin); or even the full Greek Festival Cycle. Medieval mosaics in western Europe
The prestige, both cultural and political, enjoyed by Byzantium in the Middles Ages led to a widespread imitation of its arts. Art objects in great number were imported to the West from Constantinople and other Greek centres. Individuals or communities outside the realm of Byzantium, however, were able to secure Byzantine artisans for the execution of monumental mosaics. Abbot Desiderius of the abbey of Montecassino in Italy, for example, called specialists in many crafts from Constantinople to decorate his new basilica (dedicated 1071 ce). Among these were mosaic workers. Of particular importance is the fact that he took care to see that young local artists were trained by the foreigners. This was the pattern that was followed where Byzantine experts were temporarily called in.
The Norman rulers of Sicily, who vied with the Byzantines for control of the Mediterranean, molded their representational arts largely on those of the great Eastern power. The existence, at Palermo, of a central-plan church (Martorana) embellished according to the classical system has already been noted. In other 12th-century churches in Sicily, the Byzantine element is blended with western Mediterranean traits. Cappella Palatina, the palace chapel of the royal residence at Palermo (c. 1143 and later), for example, is a synthesis of a centralized middle Byzantine church and a basilica. The building therefore called for a hybrid program. According to Western custom, the mosaics of the basilical parts depict narrative cycles: scenes from the Old Testament and from the lives of Saints Peter and Paul. In the centralized part of the church most of the features belonging to the classical system are at hand. There is a bust of the Pantokrator in the dome, surrounded by angels, but as a concession to the longitudinal disposition of the church, the Pantokrator reappears in the apse.