ATTACK AND DEFENCE. 165 



means of which the besiegers can look into the places-of-arms of the 

 covered-way. The saHents being reached, the crowning of the covered-way 

 is established, parallel to the crest of the same, and here the breaching 

 batteries are placed {jig. 2), by means of which the revetment wall of the 

 front of attack, the salients, L, of the ravelin, the two bastion salients, AA, 

 and the two shoulder angles, BB, are sought to be destroyed. The covered 

 way being cleared of the enemy, subterranean galleries, mn and wn {fig. 3), 

 are dug, leading out from the crown to the bottom of the ditch, or to the 

 level of the water in it, and the descent into the ditch is begun, from which 

 the passage of the ditch is effected, either by a covered- way, or by means 

 of a dyke or a bridge. The breach being reached, a lodgment is effected, 

 upon it, and from thence upon the different works to be taken. 



1. Works of the Trenches. The lines by means of which a siege 

 is carried on must, as they are constructed under fire of the enemy, be 

 very hastily made. The slopes towards the foe remain un worked ; the 

 interior ones, however, must be very steep, wherefore they are supported 

 usually by gabions. The trenches nearest the fortification are called saps, 

 of which there are various kinds. 1. The Uncovered sap is a simple ditch, 

 3 feet deep and 18 feet wide, having, on the side towards the enemy, a 

 parapet with a banquette. 2. The Flying sap is carried on under cover 

 of gabions, 3 feet high and 2 feet in diameter, placed by the laborers imme- 

 diately along the trace. Upon the gabions, fascines or sand-bags are 

 placed, until the parapet is 4|- feet high. The ditches are 3 feet deep, and 

 9 feet wide at the bottom. A banquette, 1 foot wide, is constructed. 

 3. The Half sap has no banquette, and there are only gabions, filled with 

 earth, sap-fagots, or sand-bags. 4. The Full sap. For this, each sapper 

 brigade consists of four men. The first rolls before him a sap-gabion, A 

 {pi. 48, fig. 5, view and ground plan), sets up the gabions x, side by side, 

 towards the fortification, and digs the ditch, y, 1 J feet wide and 1|- deep ; 

 the succeeding sappers deepen and widen the ditch each 6 inches, and 

 place between the gabions sap-fagots, p. Ordinary laborers then complete 

 the ditch to 3 feet deep and 18 feet wide and place the fascines, z. 5. The 

 Old sap {fig. 6) is also cut in steps by four sappers following each other ; 

 its ditch is 4 feet deep and 6 feet wide ; the earth is employed for the 

 parapet, B. When the old sap is employed to cut into the parapet of a 

 hostile work, the ditch is made only half as wide, and at the foot of its 

 parapet two sand-bags, z, are laid one upon the other, for a banquette. A 

 blind of fascines is also established upon the parapet. 6. The Covered sap 

 {fig. 7) consists of two full saps. A, running parallel to each other at 4 

 feet distance, over which, after the masses of earth, M, are thrown out, a 

 cover of beams, k, is laid, and thereupon fascines and sand-bags, and, 

 finally, a layer of earth, D. 7. The Single traverse sap {fig. 8) is a full 

 sap, A, which advances, not in a direct line, but in rectangular or snake- 

 like turns. It is constructed like the full sap, but as it is usually employed 

 for crowning the covered-way, the traverses,*, are placed in it. At the 

 securest points are made ramps, x, in the rearmost slope of the trench. 

 8. The Double traverse sap {fig. 9) consists of two single ones, running 



ICONOGRAPHIO ENCYCLOPiEDIA. VOL. III. 41 641 



