COMMUNICATION LINES. All the trenches are connected by communication trenches or _boyaux_, which conceal from the enemy the movements of troops. These are mere ditches about two yards deep, the earth from which is thrown out to the left and right, or on one side only. They follow a zigzag line so as not to be exposed to enfilading fire, or, when straight, are protected at intervals by earth screens (_pare-éclats_). [Illustration: Diagram of Campaign Intrenchments.] The depth or breadth of these “ditches” depends on the use to be made of them. For instance, those intended for carrying out the wounded must be deep and wide. To preclude obstruction during attack, and to provide free and quick passage for reserves rushing up from the rear, communication trenches should be very numerous. Some should be designated for forward and some for rearward movement. Each one should bear a name or a number and at its extremities arrows should indicate the direction of the circulation. Thus confusion will be avoided. TRENCHES OF ATTACK. When the opposing lines are sufficiently far from one another, it is impossible to launch an attack without having brought the infantry within striking distance. For this purpose a sufficient number of _boyaux_ are dug in the direction of the enemy, starting from the advanced trenches, passing under the wire entanglements, and connecting together with a cross-trench when at the required distance. This is the “trench of attack” and at the proper time, steps are made in it to facilitate the egress of the troops at the moment of assault. This work is done at night, and preferably, when possible, by troops which are not to take part in the attack. The men proceed to this work under cover and patrol guard. ARTILLERY. The artillery, according to its size, is placed between the lines or behind them. Field batteries are pushed forward up to the “artillery protecting line” and placed in position to shell, at any time, certain designated portions of the enemy’s front. They are either buried in the ground or sheltered under casemates, when the latter can be concealed from the enemy. The trench-guns are, generally, on account of their small range, placed in the first-line support trenches. The heavy artillery, farthest back of all, is drawn up in echelons according to its size and the part assigned to each part of it. WIRE ENTANGLEMENTS. The width of the wire entanglements varies considerably. Well-strung wire prevents any attack, and none can be attempted until the entanglements are destroyed. In front of their new lines on the Aisne, where the Germans are simply holding the ground, and have given up all notion of advance, they have stretched eight or nine successive rows of wire, each row being fifty metres wide.