424 FORTIFICATION in lines 4 feet apart, and connected together by strong wires passing through the bridging holes. FIG. 7. Gabions as an Entanglement. Crows Feet (fig. 8) are made of iron with four points so arranged that one shall always project up ward in whatever manner they may be thrown on the ground; the points are either 2 or 4 inches long. Crows feet are soivn over a space about 1 2 feet broad. Troops coming suddenly, and in the dark, on these obstacles, would be much annoyed by them. They are most effective against cavalry, and were formerly much used, more so than FIG. 8. Crows now. Feet - Trous-de-loup are holes in the ground in the form of an inverted cone or square pyramid, the sides of which are as steep as is consistent with the stability of the soil. They are made 6 or 8 feet in diameter and 6 feet deep, so that an enemy cannot use them as shel ter pits to fire from. At the bottom is fixed--, a sharp stake 3 feet long, or the branch of a tree cut into sharp points, or a num ber of smaller sharp pickets, or a quantity of crows feet. Fig. 9 shows, in plan and section, the arrangement of trous-de-loup proposed by Wenzel. If along the line of a position, either on the glacis or on the escarp (when gradually sloped as in fig. 2), small trees or Fr - 9. Plan and section shrubs are planted, they can be Trous-de-loup. on an emergency cut down, and with the points of their stumps sharpened they would become very annoying to an assailant. Harrows and many other substitutes can also be used; indeed every expedient which ingenuity can sug gest should be adopted by the engineer to check the pro gress of an advancing enemy, and to delay him as long as possible under fire. Stockades. Before proceeding to the investigation of the principles which should regulate the relief and thickness of ordinary parapets, viewed in reference to simple defensive lines and to direct fire, it is right to notice the " Stockade" as a substitute, and in some circumstances an advantageous substitute, for a parapet. The Stockade is formed of one or more rows of stout palisades, and in its simplest form is thus constructed. A row of very strong palisades, usually pointed at the top, from 9 to 12 inches in diameter, is fixed deeply in the ground, with intervals of about 3 inches between the palisades. These intervals are filled by smaller palisades cut square at the top every alternate palisade being shortened 4| inches, so that the open space above it may be used as a loophole. A stout riband nailed hori zontally to the upper ends of the palisades strengthens the construction materially. Such a Stockade is shown in plan, elevation, and section in fig. 10 ; it has a banquette of earth, which may be replaced when desirable by a wooden step. By cutting out the triangular portion shown in the section, and throwing the earth up against the front of the palisades, as indi- cated by the dotted lines, an exterior slope and escarp are formed which keep an enemy constantly in view. A stockade of this description placed close to the ed^e of FIG. 10. Plan, elevation, and section of Stockade. a steep bank, has this great advantage over a parapet, that the men behind it have a more effective command of the ground before them when firing through the loopholes than they could possibly have when firing over a parapet. It is here supposed that artillery fire cannot act directly against the stockade, but artillery may possibly be placed to act against it in a longitudinal direction, or, as it is termed, to enfilade it, and in this case the line of stockade should be interrupted by traverses, which are usually banks of earth placed transversely to the line they are intended to protect from such artillery fire. Fig. 1 1 shows a stockade of this description applied to the defence of precipitous ground. When stockades are formed into inclosed works, they are called "Tambours." Under some cir cumstances it may be desirable to throw an ordinary parapet forward to the edge of a bank, Fla "--Stockade on steep ground. the slope of which supplies the function of escarp, and hence to dig the ditch behind instead of before it, as in fig. 12, where it will be also observed that the slope of the banquette Fig. 12. is broken into two steps, the tenacity of the earth when first excavated allowing it to stand firm ; the principle of this ex cavated form of structure is adopted in sunken batteries. Sometimes the object of the parapet is merely cover and not active defence, in which case the banquette is omitted as in fig. 13, and the work is called an " Epaulement." In this profile it will be observed that a space is left between the face of the epaulement and the internal ditch. Such a space should always be left, whether the ditch is within or without, when the work to be formed is of any considerable elevation, as it affords a stage upon which the builders can stand, and lessens the height to which the diggers have to
