The trenches are of different dimensions; nevertheless, when time is not limited for their construction, Fig. 3 can be considered as representing the most generally adopted type. The earth thrown up in front, either loose or filled into sandbags, forms the parapet. As the action of the weather, especially rain, tends to cave in the sides of the trenches, they have to be upheld with wooden props, or with wire nets, supported at three or four metre intervals by wooden or iron posts. [Illustration: _FIG. 2_] [Illustration: _FIG. 3_] In the very damp regions small drains (_rigoles_) and cesspools have to be dug to carry off the water, and the trenches themselves must be provided with open “boardwalk” flooring. When not pressed by time and scarcity of material, especially in winter, all possible means should be adopted to prevent the men from standing too long in water. Dampness, more than cold, is responsible for frostbitten limbs. [Illustration: _FIG. 4_] In the parapets of trenches that are expected to last some time, loopholes are made by inserting pieces of sheet-steel with openings to allow the passage of a gun barrel. Each opening closes with a small door which remains shut except when the loophole is in use (Fig. 4). [Illustration: South-east of La Bovelle Farm February 10, 1917--2.30 P.M.] When neither time nor material is lacking, the machine-gun shelters (Fig. 5) in the trenches are installed within steel cupolas, which are either stationary or revolving. The mechanism of the latter is, however, complicated, and too delicate for use in the first lines. These cupolas are also much used for observation posts, and, as we shall see later, they are kept as much as possible concealed from the sight of the enemy by camouflage. [Illustration: _FIG. 5_] The first line comprises three positions or trenches. That nearest to the enemy is the advanced trench, and at a short distance behind it are the support trenches. Only a few men are now posted as sentries in the advanced trenches. In front of these trenches, “listening” or “watch” posts are hidden in the ground. Between these posts and the advanced trenches barbed wire entanglements are stretched, in number and width proportionate to the dangers threatening the position. In the support trenches are the dugouts sheltering the men against the fire of the artillery. Many communication trenches or _boyaux_ connect them with the advanced trenches, facilitating the rapid occupation of the latter in case of need. In the advanced trenches are built shelters for the machine-guns. Rifle-fire is directed through loopholes protected by the steel plates above mentioned (Fig. 4) which are bullet-proof at fifty yards.