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.