ROMAN ARCHITECTURE. II5 classical column eventually came to be used alone, and through the basilica, was finally utilized in a pointed form m the construc- tion of those magnificent vaulted Gothic cathedrals, which were erected in the Middle Ages. Greek buildings (see page 102) were normally only one story in height, but owing to the varying needs of the Romans, buildings of several stories were erected by them. The orders, usually attached and superimposed, were chiefly decorative features ceasing to have their true constructive significance (No. 62 a). The Thermae or Baths, Temples, Amphitheatres, Aqueducts, Bridges, Tombs, Basilicas, and Fora, are all monuments of Roman greatness, showing great constructive and engineering ability com- bined with a power to use the materials at hand with the best possible results. The Greek method of building with large blocks of stone, unconnected with mortar, was employed in the buildings of the Republic. The practical spirit of the Romans, however, urged them to make a more economical use of materials, and instead of composing the walls of their monuments of squared-blocks of stone, they inaugurated the use of concrete, a material consisting of small fragments of stone or quarry debris mixed with lime or mortar. These materials, not being special to any country, were used with success in every part of the Empire, and gave a similarity to all Roman buildings. The craftsmanship required, under the direction of the central authority, was perfectly simple ; for only rough labour, both plentiful and cheap, was required for mixing the materials of which the concrete was made, and spreading it to form the walls. The structures could be erected by hands quite unused to the art of building ; thus the Romans employed the slaves of the district, subjects liable to statute labour, or even the Roman armies; while the legal punishment of condemnation to work on public buildings was largely enforced. The Romans by their extended use of concrete founded a new constructional system and employed it in the most diverse situations, adapting it with rare sagacity to their new needs, and utilizing it in the most important projects. The various kinds of walling may be divided into two classes : — opus quadvatum, i.e., rectangular blocks of stone with or without mortar joints, frequently secured with dowels or cramps, and concrete nnfaced or faced, used especially in Italy. As stated, this was a building mixture formed of lime and lumps of tufa, peperino, broken bricks, marble or pumice stone, and from the first century b.c. was used extensively for various building purposes. (rt) Unfaced concrete was usually used for foundations, and [h) faced concrete for walls. The latter was of four varieties : — i. Concrete faced with "opus mcertum " (No. 46 b), which was the oldest kind, the concrete backing being studded
