The most obvious means of doing this was by building the arches in _rims_, as we do our brick arches--a deep arch, consisting of several distinct arches laid one over the other, each forming the centre on which the next is built (Fig. 136). By this mode of building an arch of any degree of strength may be built of stones of the most moderate dimensions. This system, consequently, became general in the Romanesque buildings. [Illustration: Fig. 136.] [Illustration: Fig. 137.] Now, a deep arch so constructed, and built square through the wall, has a heavy clumsy appearance, and forms a dark and cavern-like recess. You may ornament the voussoirs and vary their colour as you please, but still it is heavy, wanting in play of light and shade, and obstructive to the free passage of the rays of light. This was early felt and early obviated. In an arch built in several rims, it is not necessary that any but the outer rim should be of the full width of the wall. This suggested the system of _sub-ordinating_ the rims, or recessing them, one behind the other, so as to divide the arch into what are called _orders_ (Fig. 137). This gives us at once a new and beautiful mode of arching, economical, and adapted to all varieties of material, giving great play of light and shade, offering the greatest freedom for the admission of light, and suggesting (as we shall see) a perfectly new system of decoration. This division of the arch into receding orders necessitated a corresponding form in the piers which supported it. [Illustration: Fig. 138.] [Illustration: Fig. 139.] [Illustration: Fig. 140.] The first means of relieving the plainness of this block form was the introduction of an impost at the springing, defining the line which separates the pier from the arch (Fig. 138). Afterwards the orders of the jamb would receive pilaster capitals (Fig. 139), and finally decorative columns would be inserted in their place (Fig. 140), thus completing the general idea of the pier and arch as made use of during the Romanesque period. The arch itself was at the same time subjected to various systems of decoration suited to its _normal_ construction. It is clear that the extreme angles of the orders contribute but slightly to their strength. These might, therefore, be rounded, chamfered, or moulded at pleasure. It became common to form them into large rolls between two hollows, and also to cut the order into various mechanical or other forms, as zigzag, etc. etc., according to the fancy of the architect, from which arose the whole system of Romanesque arch-decoration; and as the junction of the arch with the wall above was but slightly marked by the change in the direction of the joints, a small projecting moulding was introduced between them, which we call the dripstone or label, which not only drew the line more emphatically but also served to prevent the water which ran down the face of the walls from discolouring the arch-mouldings.