[Illustration: FIG. 14.--Romanesque Arch.]
of order and regularity were introduced into the system of construction. The large and massive building materials employed by the Romans not being usually available by the builders of the Middle Ages, smaller materials had to be utilised, and this led to the introduction of new ideas in their application. For instance, the arches supporting walls were, under the Romans, constructed with large materials, and had a broad soffit or under surface going through the wall (Fig. 13); but with the smaller materials in use in the tenth and eleventh centuries, arches, for the same purpose, were more conveniently built in rings, one within the other (Fig. 14). These rings were placed so as to present to the eye, instead of a flat soffit, a series of arches arranged in stages or steps towards the centre, and each bearing a part of the load of the wall. This subdivision of the original plain soffit is called the “subordination” of arches, and was the first step in the long process of advance which led finally to the perfect Gothic architecture of the Middle Ages.
The next step was to divide the solid square piers which had been originally employed to support the arches into a number of distinct parts corresponding to the rings of the arches, thus forming “orders” in the piers, as well as in the arches they carried. (See Fig. 14.)
[Illustration: FIG. 15.--St. Trophime, Arles.]
Owing to the occurrence of frequent fires in the wooden roofs of early churches, the builders aimed at carrying out the Roman practice of fireproof vaulting. This was at first done timidly and with many failures. The round barrel vault of the Romans was that generally employed; but in Provence the pointed barrel vault (Fig. 15) was adopted from an early period, being a form which exerted on the side walls a less horizontal thrust than the semi-circular arch, and was the best shape for supporting a stone roof laid upon it. In order to strengthen this vault, a projecting ring or inner arch was constructed under the main vault, and extended across the nave between each pair of the main piers.
Carrying out the principle of subordination already introduced, each of these strengthening rings had a shaft with cap and base placed so as to receive it, thus indicating to the eye the principle on which it acted--viz., that of carrying the weight of the strengthening rib down to the foundation.