In _Roman_ architecture, then, as stated, the arch-construction and vaulting is of very common occurrence, or rather we have certain remains which we can only attribute to the age of the Roman kings, if we may fully believe the evidence of later times. Of this type are the catacombs and cloaca, which were vaulted, but must be regarded as works of a more recent restoration. The most probable discoverer yet suggested of the vault is Democritus[103], who occupied himself in a variety of ways with mathematical problems and is held to be the discoverer of lithotomy.
One of the most famous buildings of Roman architecture, in which the circular arch appears as fundamental type is the Pantheon of Agrippa dedicated to Jupiter Ultor, which, in addition to the statue of Jupiter, contained colossal images of gods in no less than six other niches, namely, Mars, Venus, the deified Julius Caesar as well as three others whose identity we cannot fix with accuracy. In either side of these niches stood two Corinthian columns, and the whole was vaulted with one majestic vault in form of the half globe and corresponding to the vault of heaven. With reference to the material of this vault we may note that it is not a stone one. In other words the Romans, in the majority of their vaultings, in the first instance carried out a construction of wood, and covered the same with a composition of chalk and puzzolana cement, which was made of the dust of a light kind of tufa and broken tile shards. When this composition was dry the whole was formed into a mass so that the wooden scaffolding could be removed and the vaulting, by virtue of the lightness of its material and the stability of its consolidation, exercised only an insignificant pressure on the walls.
(_c_) The architecture of the Romans possessed moreover generally, and apart from this novel employment of arch construction, an entirely different scope and character than that of Greece. The Greeks distinguished themselves, while carrying throughout their work its main purpose, and by virtue of their perfection as artists, in the nobility, the simplicity no less than the airy delicacy of their decorations. The Romans on the contrary are, as artists, at least on the mechanical side of construction more rich and more ostentatious, but at the same time of less nobility and grace. Add to this in their architecture we meet with a variety of intention which was unknown to the Greek. As I have already observed the Greeks entirely devoted the splendour and beauty of art to public objects. Their private dwellings remained insignificant. Among the Romans, however, not only do we find an increase of public buildings, whose main purpose of construction was splendidly embellished in theatres, spaces for animal combats and other means of public sport, but architecture received a deliberate impulse in the direction of private use. More especially after the civil wars villas, baths, colonnades, flights of steps were constructed with the imposing character of the most luxurious extravagance, and by this means a new opening was made for the arts of building, which also included that of gardening, which was perfected in a way that evinced very considerable talent and taste. The villa of Lucullus is a striking example.