the buttress, the Romans had employed a kindred principle, though in a most rudimentary way. They had constructed a framework of masonry to give strength to their vaults, [1] but with them this framework was buried in the thickness of the masonry instead of projecting from, or even appearing upon, its surface. It consequently failed to possess the important use of the rib system we are now considering, which, being quite independent of the vaults, serves as a strong centring, and prevents any rupture that may by any chance take place in one cell or compartment of the vault, from communicating itself to others. In addition to this, the employment of an independent support for each rib and arch to be carried—which constitutes the functional grouping of supports above spoken of—completed the structural improvements devised by the Romanesque builders.
We are yet far from the Gothic system. The inert principle of construction, the massive walls, the small apertures, and the horizontal lines of the Romanesque architecture make it still closely akin to the old Roman style. But there are rudiments in it already quickening with latent life, which will completely transform the Romanesque building. The evolution of the Gothic system consisted in gradually perfecting the rudimentary skeleton, so as to make it an independent structure. To every part a complete and independent working efficiency was to be given, and an appropriate artistic, as well as a mechanical value. All this was rendered possible to a far greater degree than it could otherwise have been by the introduction of the pointed arch, not as an ornamental feature in doors and windows, but as a constructive device in vaulting.
The properties of the pointed arch which enabled the Gothic builders to overcome difficulties in vaulting that had before been insuperable are that it exerts a less powerful thrust than the round arch, and that with a given span its crown may be made to reach any level. Its employment in the transverse arches of the vault raised their crowns so that, with arches of full semicircular sweep for the diagonals, the thrusts were greatly diminished. The vaulting of oblong compartments had before been attended with difficulties resulting from the fact that the height of the crown of a
- ↑ See Choisy, L'Art de Batir chez les Romains.
