Vaulting
The most significant development in building was the Arch and subsequent vaulting, by means of which extensive covered areas were rendered possible. The Pantheon at Rome is covered with a hemispherical vault or dome 139 feet in diameter.
No. 26. Section and interior elevation of Pantheon, Rome.
The dome, which is interiorally occupied by radiating and horizontal ribs, resulting in five horizontal rows of cassons, or coffers, is really a casting in cement; and in principle is identical with the present method of building, in which concrete or cement forms a considerable part in construction.
Apart from other reasons, the Arch was necessitated by small material, which, in the case of the Lintel, could not be employed without the device of joggelled joints. In the absence of suitable material to cover spans, it became necessary to devise some means to the desired result. This was achieved by bridging the span with separate pieces of material cut to the necessary wedge form.
The Arch was first applied to such useful and necessary buildings as the Cloaca Maxima, to aqueducts, bridges, and viaducts, from which its firm construction and power of resistance were found to be applicable to buildings of many storeys.
No. 27. Coliseum, Rome. Section and part elevation showing arch and vault construction.