If the forces be sufficiently numerous to fight by _corps d'armee,_ each corps should have its own reserve, independent of the general reserve of the army. Again, if the forces be so small as to act by grand divisions only, each division should then have _its_ separate reserve. An army, whether composed of separate corps or of grand divisions, usually forms, on the field of battle, a centre, two wings, and a reserve. Each corps or division acts by itself, with its infantry, cavalry, artillery, and engineer troops. The reserve of cavalry may be formed in rear of the centre or one of the wings. In small forces of fifty or sixty thousand men, the cavalry may act with advantage on the wings, in the manner of the ancients. If the reserve of this arm be large enough to form three separate bodies, it may _itself_ very properly be formed into a centre and wings. If it be formed into two columns only, they may be placed in rear of the openings between the centre and the wings of the main force. The reserve of artillery is employed either to reinforce the centre or a wing, and in the defensive is frequently distributed throughout the whole line of battle. In offensive operations, it may be well to concentrate as much fire as possible on the intended point of attack. The mounted artillery either acts in concert with the cavalry, of is used to reinforce that arm; the light-foot acts with the infantry, and the batteries of heavy calibre are distributed along the line, or concentrated on some important point where their fire may be most effectual. They reach the enemy's forces at a distance, and arrest the impulsion of his attack. They may also be employed to draw the fire of his artillery; but their movements are too slow and difficult for a reserve. The order of succession in which the different arms are engaged in a battle, depends upon the nature of the ground and other accidental circumstances, and cannot be determined by any fixed rules. The following, however, is most frequently employed, and in ordinary cases may be deemed good.