In Roman works, the arched construction was in many cases studiously overlaid and concealed by the decorative features of trabeated architecture; and, where an arch was architecturally treated, it was for the most part by bending round it the mouldings of an architrave or _beam_: and, where a vault was rendered ornamental, it was often by repeating on its coved surface the coffered panels which had originated in a horizontal ceiling; while, in purely arcuated works, such as the stupendous aqueducts, architectural decoration was usually ignored, and structural grandeur alone trusted to for beauty. Still, however, enough was done to convince us that these great builders were on the high road to a noble solution of the problem, and were only, by external accidents, stopped short of its attainment. I am not about to indulge in abstract imaginings as to what an arcuated style of architecture might be if originated without the aid of previous associations or traditions; but I would ask you to follow out, with some reference to the previous Classic styles, and aided by our knowledge of subsequent developments, the _rationale_ of such a style as that whose leading conditions I have stated. We must begin with the simplest elements of the style. Firstly, then, let us take a mere opening in a wall, whether intended for a window or for any other use. As in the trabeated system, apart from architecture, such an opening would be covered by a single block of stone (Fig. 274), so in an arched system would it be bridged over by an arch (Fig. 275); and, just in the same manner, if a continuous series of openings were required, equivalent to a colonnade, the same simple idea would be repeated,--in the one system horizontal stones lying upon upright ones (as at Stone House) or upon piers (Fig. 276), and in the other the openings being covered by a series of arches (Fig. 277); the _colonnade_ being the ultimate result in the one case, the _arcade_ in the other. [Illustration: Fig. 274.] [Illustration: Fig. 275.] [Illustration: Fig. 276.] [Illustration: Fig. 277.] [Illustration: Fig. 278.] [Illustration: Fig. 279.] [Illustration: Fig. 280.] To architecturalise the arched opening, or the continuous arcade, the simplest expedients seem to be the insertion between the pier and the arch of an impost moulding to mark the springing line (Fig. 278); and, in the arch, either to individualise the arch-stones by chamfering their edges, as the Romans often did, or to relieve their plain surface by moulding, the latter being best suited where the stones made use of are of only moderate size (Fig. 279). The mouldings of the arch may, however, be continued down the jambs without an impost, and in either case a projecting rim or hood-mould may be introduced over the main arch to emphasise the line which separates the arch from the superincumbent wall (Fig. 280). [Illustration: Fig. 281.] [Illustration: Fig. 282.]