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  The arch entered into almost every structure, public or private, and superseded the use of long stone-beams, which were necessary in the Grecian temples, as also of wooden timbers, in the use of which the Romans were not skilled, and which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.

The extensive application of the arch doubtless led to the deterioration of the Grecian architecture, since it blended columns with arcades, and thus impaired the harmony which so peculiarly marked the temples of Athens and Corinth; and as taste became vitiated with the decline of the empire, monstrous combinations took place, which were a great fall from the simplicity of the Parthenon and the interior of the Pantheon.