These traverses are usually made at least 20 feet in length. They can be used only when good drainage can be secured. =36.= =Crowning the Covered Way= (Pl. IV., Fig. 36).--The traversed sap is used for “_crowning the covered way_,” which consists in constructing a battery or infantry parapet along the crest of the covered way, from which a fire can be brought upon the ditch and the scarp-wall of the work. To accomplish this the sap is run parallel to the crest, with its nearer cutting line 18 or 20 feet from it. For an infantry trench the traverses may be of the dimensions already given. To cover a battery they should be about 33' long. It will generally be necessary to use the double sap altogether in their construction, but usually the earth excavated by Nos. 3 and 4 of both brigades will be thrown on the parapet next the work, the parapet on the reverse side formed by Nos. 1 and 2 affording sufficient cover for constructing the sap and traverses. The parapet is prepared for infantry fire as described for the parallels. The emplacements for guns, the service magazines, etc., etc., are prepared and the embrasures are cut, or the parapet prepared for the overbank carriages at the last moment, under cover of the small-arm and machine-gun fire from the parallels and places of arms, and the artillery fire from batteries, which do not endanger the working parties. =37.= =Trench Cavalier.=--In order to obtain a greater plunge upon the covered way and ditch, short lengths of double sap are sometimes run at right angles to the direction of the crests of the covered way at about 30 yards outside its salient. The parapet on the side of the sap towards the work is thrown forward and built up to the desired height with gabions and sand-bags, and provided with steps and sand-bag loopholes, giving a short length of parapet with considerable command, firing directly along the covered way at short range. This construction is called a _Trench cavalier_. It will be seldom, if ever, used in the future. =38.= =Former Methods of Sapping.=--Before the general introduction of machine and rapid-fire guns and of small arms of extreme accuracy and penetration saps were constructed by No. 1 sapper driving a trench 18" × 18", which was enlarged successively by Nos. 2, 3, and 4. Cover for the sappers was obtained by the use of a sap-roller (a large gabion, 7' 6" long and 4' in diameter, stuffed with fascines and rods) as a movable head parapet, and the construction of the side parapet was expedited by the use of gabions, sap-fagots, etc. This method cannot be used against an enemy well equipped with modern weapons. It is referred to only as a suggestion that a readily improvised modification of it might be used to capture, with the least possible loss, a party of rioters, criminals, or other badly-armed men occupying an isolated house or other cover. PASSAGE OF THE DITCH.