If painting under the new conditions entered on a fresh course of power and conquest, if it set itself successfully to provide an imagery for new and intense thought, sculpture, on the other hand, seems to have withered away as it became removed from the classic stock. Already in the pre-Constantinian epoch of classical art sculpture had become strangely dry and powerless, and as time went on the traditions of modelling appear to have been forgotten. Two points of recent criticism may be mentioned here. It has been shown that the porphyry images of warriors at the southwest angle of St Mark's, Venice, are of Egyptian origin and are of late classical tradition. The celebrated bronze St Peter at Rome is now assigned to the 13th century. Not only did statue-making become nearly a lost art, but architectural carvings ceased to be seen as modelled form, and a new system of relief came into use. Ornament, instead of being gathered up into forcible projections relieved against retiring planes, and instead of having its surfaces modulated all over with delicate gradations of shade, was spread over a given space in an even fretwork.
Such a highly developed member as the capital, for instance, was thought of first as a simple, solid form, usually more or less the shape of a bowl, and the carving was spread out over the general surface, the background being sunk into sharply defined spaces of shadow, all about the same size. Often the background was so deeply excavated that it ceased to be a plane supporting the relieved parts, but passed wholly into darkness. Strzygowski has given to this process the name of the "deep-dark" ground. A further step was to relieve the upper fretwork of carving from the ground altogether in certain places by cutting away the sustaining portions.
The simplicity, the definition and crisp sharpness of some of the results are entirely delightful. The bluntness and weariness of many of the later modelled Roman forms disappear in the new energy of workmanship which was engaged in exploring a fresh field of beauty. These brightly illuminated lattices of carved ornament seem to hold within them masses of cold shadow. Beautiful as was this method of architectural adornment, it must be allowed that it was, in essence, much more elementary than the school of modelled form. All such carvings were usually brightly coloured and gilt, and it seems probable that the whole was considered rather as a colour arrangement than as sculpture proper.
Plaster work, again, an art on which wonderful skill was lavished in Rome, became under the Byzantines extremely rude. Many good examples of this work exist at San Vitale and Sant' Apollinare in Classe at Ravenna, also at Parenzo, and at St Sophia, Constantinople. Later examples of plaster work of Byzantine tradition are to be found at Cividale, and at Sant' Ambrogio, Milan, where the tympana of the well-known baldachin are of this material, and contain modelled figures.
Coins and medallions of even the best period of Byzantine art prove what a deep abyss separates them from the power over modelled relief shown in classical examples. The sculptural art is best displayed by ivory carvings, although this is more to be attributed to their pictorial quality than to a feeling for modelling.