as the various waves of barbarians swept over the empire and settled in different parts of it, they adopted the Roman system of construction which they found in existence, and imported into it gradually ideas of their own. In course of time a method of building was thus developed which is known as the Romanesque style. This style varied greatly in different localities, according as it was influenced by the presence or absence of Roman structures to serve as models for imitation; but over the whole empire it retained a certain amount of resemblance to Roman forms. The Roman principle of an arched, as distinguished from a trabeated, style of building was preserved everywhere, but was for long applied in a very simple and merely imitative manner. When, however, nationalities came to be settled, and law established, and when at the same time the regulating and disciplining influence of the Church made itself felt, some elements [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.]