until at length, finding it utterly impracticable to force any part of even the first line, they were obliged to retire from Portugal, closely followed and harassed by the army which they had previously driven out of Spain. Yet perfect as were the lines of Torres Vedras, and though one of the ablest of the French generals and a veteran French army were foiled before them, it is not meant to infer that the system of separate field-works is a model to be followed on all occasions; for, though the old method of covering a considerable front by a continued line of regular bastions and curtains has been generally condemned by modern engineers, there may be situations where the application of continued lines may be judiciously made. There is no fixed rule; the nature of the ground and of the position to be defended must determine the proper description of works.

But as in defence artillery should be combined with musketry, it is necessary that in the arrangement of lines provision should be made for the use of cannon; and as they should be preserved for action at the right moment, they should, when practicable, be mounted on carriages of such a height as will enable them to give their fire over a full parapet, the gun and carriage disappearing below the parapet after the fire is given, so that the loading may be effected in security. In particular cases, such as in flanks where

Fre. 32.-Embrasures and Barbettes.

the lateral range of the guns is restricted, and where the guns are not exposed, or are exposed to indirect fire only, openings in the parapet called "Embrasures" may be made use of, but they have many serious disadvantages:-they weaken the parapets; they offer distinct marks to the enemy; they are easily blown down by shells; they are de

stroyed by the fire of their own guns; they are difficult to construct, and still more difficult to maintain. The interior opening called the "Throat" of the embrasure made wide enough to admit the muzzle of the gun, about 20 inches; the width of the outer opening called the "Mouth" is determined by the lateral range of the gun, which should not exceed 20°. The slope of the bottom of the embrasure, called the "Sole," is determined by the object upon which the fire of the gun is to be directed. When required for indirect fire only, the sole is made countersloping; by this arrangement the exposure of the gun detachment is considerably lessened, and, in order to diminish still further this exposure, the sides of the embrasures are made with a winding slope,-steep at the throat, from 6 to 1 or less, and flattening out at the mouth to 1 to 1. As a rule, embrasures should not be made till they are required, so that the parapet may be made solid in the first instance (see fig. 31).

er,

The portion of parapet below the embrasure is called Genouillère (from genou, the knee), and should be 2 feet 5 inches high; the portion between two embrasures is called a Merlon, from the Italian merlone, a battlement; the bottom of the embrasure is called its Sole; and, as has been suggested in respect to the superior slope of the parapet, it may be horizontal for the first two feet from the neck, and then slope downwards as much as may be necessary for the depression required in firing. The direction of the embrasure depends on the direction of the line of fire; it may be either perpendicular to the crest or oblique. In the latter case, should the obliquity be very great, or exceeding 70°, the crest of the parapet must be made re-entering, so as to strengthen it near the neck, and to enable the gun-carriage to be brought up square to the parapet. The sides of the embrasure are called Cheeks, and should be revetted with sods, fascines, gabions (cylindrical baskets made of wickand filled with earth after they are in position), sand

FIG. 33.-Construction of a Barbette in a Salient.

bags, planks, or hurdles. In fig. 32, on the left, at B, a direct embrasure is seen cut straight through the parapet; and on the right at A, an oblique one, both being intended to enfilade the ditches opposite them; and it will be observed that, from the obliquity of the right-hand embrasure, the interior of the work becomes so much exposed, that a traverse, T, behind the embrasure, becomes necessary. Barbettes are also shown in this figure-one at the salient at D for four guns, and another at C, perpendicular to the face, for two. The terreplein of the Barbette should be 34 feet below the crest of the parapet; its length from front to rear from 18 feet to 20 feet; and its breadth, for a single gun, from 15 feet to 18 feet, according as it may be necessary to fire more or less obliquely; a breadth of 15 feet should be added for each additional gun. To add to the lateral sweep or range of the gun, without diminishing the banquette, or, in other words, the musketry fire, the barbette may be made wider in the rear than in front. In proportion to its magnitude should be the number of "Ramps," or slopes of approach; as, for example, at C only one, at D three. The ramps should be from 8 to 9 feet wide, and their slopes should have bases equal to 4 times the height of the barbette. The lateral slopes of the barbette and of its ramps should be revetted whenever it is

possible to obtain sods, fascines, hurdles, or other materials suited for the purpose, in order to economize space in the work, as the base of the slope may be then reduced to onefourth or one-sixth the height; when unrevetted they have slopes of one-sixth. The terreplein of the barbette may require, as at C, to be covered in flank by a traverse. The mode of constructing a barbette in a salient is exhibited in fig. 33.

At any point g of the face AB raise a perpendicular gh, either 18 or 20 feet in length, to include the amount of recoil;

FIG. 34.

at the point A thus determined raise a perpendicular to gh, and prolong it to its intersection with the other face AC at E, then setting off AF on the other face equal to AE. On the capital AD set off a double perpendicular at any point i, prolonging it both ways, and making ik and il each at least equal to 44 feet to represent the half breadth of the platform on which the guncarriage is intended to stand and move; through the points k and draw parallels to the capital, cutting the faces on the points m and n; join m, n, and parallel to the line mn draw the line OP at 18 or 20 feet distant from it, when mnPO forms the platform. Join FO and EP, and AEPOF will represent the

contour or trace of the barbette. The manner in which the orest of the parapet is formed above the salient A, and the mode in which the firing may be effected in directions perpendicular to the faces, as well as in the direction of the capital, are shown in fig. 34.

In the case of a partly sunken parapet, in which the portion above the banquette is raised above and the portion below the banquette excavated below the plane of site,-as in fig. 35, the barbette constructed in the hollow portion will enable the gun to fire over the parapet; and it should be protected by forming a bonnetted embrasure, which may be sometimes made large enough, as here represented, to hold two guns. It need scarcely be added that an engineer

ledge of the art of war opens a wide field for the exercise o the talents and resources of engineers; but the possession of a military coup-d'oeil, which comprehends at a glance the true bearing or character of objects and events is necessary for the conversion of stores of information to the best prac tical uses. In passing through a country, it requires an experienced eye to seize quickly on whatever it presents cal culated to prove advantageous or disadvantageous for attack or defence; to appreciate the value of villages, inclosures, and broken ground; to know where to dam up rivers, to scarp heights, to form abattis, trous-de-loup, and other obstacles; to select the best situations for field-forts and redoubts, and the best sites for batteries; and to arrange the defensive measures with reference to the number of troops disposable, so that the movements of the defenders may not be obstructed or retarded, and their communications may be short and easy. The variety of ground upon which military operations must be carried on precludes the possibility of laying down fixed rules in regard to this subject; the accidents of the ground, and the peculiar circumstances of each individual case, must determine the extent and description of the works to be constructed, as well as the obstacles most proper to be formed for retarding the advance of an enemy.

But though the observance of fixed rules be impracticable, general principles are of universal application, and certain maxims founded upon them hold good in the construction of field-works as much as in the erection of the complicated works of a fortress. These maxims, which are of invariable application, are (1) that the works to be flanked must never be beyond the range of the projectiles used in the works flanking them, or, in other words, that the length of the lines of defence must never exceed the effective

ought to be ready to adapt any of the expedients here briefly noticed to the circumstances of the case before him, and that a mind stored with resources against any contingency is the highest endowment of a good officer. It must be obvious that in Field Fortification even a limited know

Lines broken or with intervals............

1 Shaw's Course of Field Fortification, p. 9 seq. Much assistance has been derived from this useful work in the compilation of this article, meister, translated by Rieffel into French, the figures of which have as well as from the admirable treatise on Field Fortification, by Fisch been freely used.

The first class are of the simplest kind of field-works, | and serve as cover in front of avenues, bridges (see fig. 49), causeways, and the like; being open at the gorge, they are only used when their extremities rest on rivers, or on obstacles which prevent their being turned, or when within the full sweeping fire of works in their rear. To increase the strength of a "Redan" its faces are sometimes broken into a kind of flank, as in fig. 36. In the "Double Redan,"

FIG. 39.-Bastioned Heads.

or "queue d'hironde," fig. 37, the re-entering faces defend each other. "Tenailled Heads" (fig. 38) are used in situations which require a greater extent of front. "Bastioned Heads" (fig. 39) are also employed in similar circumstances. "Redoubts" (fig. 40) are closed works of square or polygonal figure. In square redoubts provision should be made

From 21 to 45 Yards.

FIG. 42.-Bastioned Forts.

trace of the redoubts was varied to suit the conformation of the ground.

In "Bastioned Forts," fig. 42, the flanking defence afforded by the parapets to the ditches is nearly perfect. As bastioned forts are only constructed in special cases of importance, no labor or expense should be spared in their formation. The bastioned face may be applied to any polygon

AB varies from 180 to 400 yards. FIG. 44.-Lines of Redans.

thickness to resist the fire of the heaviest guns that can be brought against them. In some cases it will be necessary that the parapets should be strong enough to resist the fire of light field-guns, whilst in others it will be sufficient if they serve as a cover to the men within them against musketry. This latter cover is that which, when time for more does not avail, is thrown up at the close of a march, after taking up a position, and which, if the army does not