This transitional style is rightly called early Christian, or Constantinian. In the East, the vital part of the empire at this time, a greater change was taking place that brought back life once again to the arts of decoration; this may be expressed in a formula as the re-orientalization of classic art--the linking of simple massive Roman building to a new decoration, vividly alive and inventive, frank, bright, and full of colour, and yet as rational in its choice and application as the construction. In the modern sense the Romans may be said to have invented building, and the Byzantine-Greeks architecture. The Roman system of arched building, covered with brick and concrete vaulted shells and domes, had been masked by non-functional pillars, tablements, and pediments in what was thought the true Athenian manner; at the same time many beautiful decorative expedients were also in use, such as the lining of walls with large thin marble slabs, or small pieces of glass of various forms and colours. Mosaic of gold glass seems to have been known before the time of Constantine.[329] Gold tesserae probably originated in an at first almost accidental use of portions of the Roman glass vessels which are decorated by patterns in gold leaf protected by a thin layer of glass over the surface. Parts of such vessels are found used decoratively in the Catacombs. Byzantine architecture was developed by the use of brick in the frankest and fullest manner, especially in domical vaulting. Wide spans were kept in equipoise by other smaller domes. The more concentrated supports were marble monoliths, and the wall and vault surfaces were covered by incrustations of marble slabs and glass mosaic. Directness, an economy of labour relative to the results obtained, is perhaps the most essential characteristic of the art both in construction and decoration in the great period. This freedom and rationality mark it out from all other styles of building, or rather make it include all other styles, for this reaches the universal. M. Choisy rightly insists on the fact that the Byzantine builders endeavoured to suppress preparatory and auxiliary work, and to execute their vaults and domes without centring. “The greater number of their vaults,” he says “rose in space without any kind of support.... Their method is not a mere variation of that of the West, but it is quite a distinct system, not even derived from a Roman source, but Asiatic. Byzantine art is the Greek spirit working on Asiatic elements.” Here we have an extreme statement in one direction, and the word Roman must be used in a narrow sense; for these Asiatic elements in construction, of which alone M. Choisy seems to be speaking, whatever were their remote origins must have been completely absorbed into the larger Rome of the Empire, and we have no knowledge of any other system of construction in western Asia from the first to the fourth century than “Roman,” unless we