§ I. I have classed these two means of architectural effect together, because the one is in most cases the negative of the other, and is used to relieve it exactly as shadow relieves light; recess alternating with roll, not only in lateral, but in successive order; not merely side by side with each other, but interrupted the one by the other in their own lines. A recess itself has properly no decoration; but its depth gives value to the decoration which flanks, encloses, or interrupts it, and the form which interrupts it best is the roll.
§ II. I use the word roll generally for any mouldings which present to the eye somewhat the appearance of being cylindrical, and look like round rods. When upright, they are in appearance, if not in fact, small shafts; and are a kind of bent shaft, even when used in archivolts and traceries;--when horizontal, they confuse themselves with cornices, and are, in fact, generally to be considered as the best means of drawing an architectural line in any direction, the soft curve of their side obtaining some shadow at nearly all times of the day, and that more tender and grateful to the eye than can be obtained either by an incision or by any other form of projection.
§ III. Their decorative power is, however, too slight for rich work, and they frequently require, like the angle and the fillet, to be rendered interesting by subdivision or minor ornament of their own. When the roll is small, this is effected, exactly as in the case of the fillet, by cutting pieces out of it; giving in the simplest results what is called the Norman billet moulding: and when the cuts are given in couples, and the pieces rounded into spheres and almonds, we have the ordinary Greek bead, both of them too well known to require illustration. The Norman billet we shall not meet with in Venice; the bead constantly occurs in Byzantine, and of course in Renaissance work. In Plate IX., Fig. 17, there is a remarkable example of its early treatment, where the cuts in it are left sharp.
§ IV. But the roll, if it be of any size, deserves better treatment. Its rounded surface is too beautiful to be cut away in notches; and it is rather to be covered with flat chasing or inlaid patterns. Thus ornamented, it gradually blends itself with the true shaft, both in the Romanesque work of the North, and in the Italian connected schools; and the patterns used for it are those used for shaft decoration in general.