The pediments (roof-angles) used in Roman architectural works are steeper than those made by the Greeks, varying in inclination from eighteen to twenty-five degrees, instead of fourteen. The mouldings are the same as the Grecian in general form, although they differ from them in contour; they are less delicate and graceful, but were used in great profusion. Roman architecture is overdone with ornament, every moulding carved, and every straight surface sculptured with foliage or historical subjects in relief. The ornaments of the frieze consist of foliage and animals, with a variety of other things. The great exuberance of ornament is considered a defect, although when applied to some structures it is exceedingly beautiful. In the time of the first Caesars Roman architecture had, from the huge size of the buildings, a character of grandeur and magnificence. Columns and arches appeared in all the leading public buildings,--columns generally forming the external and arches the internal construction. Fabric after fabric arose on the ruins of others. The Flavii supplanted the edifices of Nero, which ministered to debauchery, by structures of public utility.
The Romans invented no new principle in architecture, unless it be the arch, which was known, though not practically applied, by the Assyrians, Egyptians, and Greeks. The Romans were a practical and utilitarian people, and needed for their various structures greater economy of material than was compatible with large blocks of stone, especially for such as were carried to great altitudes. The arch supplied this want, and is perhaps the greatest invention ever made in architecture. No instance of its adoption occurs in the construction of Greek edifices before Greece became a part of the Roman empire. Its application dates back to the Cloaca Maxima, and may have been of Etrurian invention. Some maintain that Archimedes of Sicily was the inventor of the arch; but to whomsoever the glory of the invention is due, it is certain that the Romans were the first of European nations to make a practical application of its wonderful qualities. It enabled them to rear vast edifices with the humblest materials, to build bridges, aqueducts, sewers, amphitheatres, and triumphal arches, as well as temples and palaces. The merits of the arch have never been lost sight of by succeeding generations, and it is an essential element in the magnificent Gothic cathedrals of the Middle Ages. Its application extends to domes and cupolas, to floors and corridors and roofs, and to various other parts of buildings where economy of material and labor is desired. It was applied extensively to doorways and windows, and is an ornament as well as a utility. The most imposing forms of Roman architecture may be traced to a knowledge of the properties of the arch, and as brick was more extensively used than any other material, the arch was invaluable. The imperial palace on Mount Palatine, the Pantheon (except its portico and internal columns), the temples of Peace, of Venus and Rome, and of Minerva Medica, were of brick. So were the great baths of Titus, Caracalla, and Diocletian, the villa of Hadrian, the city walls, the villa of Mecaenas at Tivoli, and most of the palaces of the nobility,--although, like many of the temples, they were faced with stone. The Colosseum was of travertine, a cheap white limestone, and faced with marble. It was another custom to stucco the surface of brick walls, as favorable to decorations. In consequence of the invention of the arch, the Romans erected a greater variety of fine structures than either the Greeks or Egyptians, whose public edifices were chiefly confined to temples. The arch entered into almost every structure, public or private, and superseded the use of long stone-beams, which were necessary in the Grecian temples, as also of wooden timbers, in the use of which the Romans were not skilled, and which do not really pertain to architecture: an imposing edifice must always be constructed of stone or brick. The arch also enabled the Romans to economize in the use of costly marbles, of which they were very fond, as well as of other stones. Some of the finest columns were made of Egyptian granite, very highly polished.