Bastion forts have frequently been proposed ; but in ge neral they arc inferior to star forts. The triangular half bastion is peculiarly defective. They are difficult to con struct—the saliants .re too acute and ill-defended—the faces of the demi-lunes arc without any cover, and the in terior surface is too small. The square half-bastion is lit tle better than the triangular, but it incloses a larger space. When the bastions are full, the work may sometimes be very advantageous, and the construction is the same as in permanent fortification.
In bastion forts the sides should not be less than 100, nor more than 200 yards, that the flanked parts may be within musket shot. Perhaps 120 yards is a good medium. The best form of the curtain is to break it twice, by which a very advantageous fire is obtained.
The principal things to be considered in field fortifica tion are, the nature of the ground, aid the soil to be used, the attack that is likely to be made, the relative importance of the place, and the number of the garrison.
When the place is to be defended against small arms only, the talus may be as steep as possible, from the sum mit of the parapet to the bottom of the ditch ; the base be ing equal to the height. If guns are to be used, the slope should be greater, to make a better defence. The base, in this case, may be one-third of the height, if the earth is heavy ; one-half, if lighter ; and two-thirds, if it be sandy or -stony. To keep the talus from falling down, gazons are used wherever they can be conveniently obtained. Revete ments of various other kinds have also been used, as fas oines, saucissons, hurdles, trees, boards, &c. but no method of,constructing the talus appears so easy or so advantage ous as that already described, especially if it has a row of trees on the front, standing seven or eight feet above the ground. Sometimes it may be useful to interrupt the ta lus by a berme, so as to take the pressure of the parapet as much as possible off the counterscarpe. Care must be taken, however, that this berme be at least 5 feet 6 inches below the exterior summit of the parapet, lest the besieger take advantage of it to fire over upon the garrison. Pali .sadoes and chevaux de frises, or beams stuck full of pins, Stc. are useful on the berme, only when it is covered from the enemy's fire. The interior slope of the parapet must
be as little as possible, that the soldiers may approach close to it. From 10 to 16 inches of a base will be enough, and it ought to be lined with fascines, boards, or gazons.
The banquette behind the parapet, in a single work, should be from two feet to two feet six inches broad ; but if the work has a curtain resistance, it ought to be 4 feet in breadth, to afford a ready communication. It should also be from 4 feet to 4 feet 3 inches lower than the parapet, and have a slope or stairs of fascines towards the interior, by which it may he ascended.
All these works, when they are intended for a short re sistance, consist only of a parapet : but when they are larger, and intended to hold out for a considerable time, they have generally a small rampart, for the convenience of the artillery.
The upper slope or plonge of the parapet ought to be directed to the upper part of the counterscarpe ; or if it has a great command of the surrounding country, it may be directed somewhat higher, as the slope should never be more than from two to three inches in the foot, lest the up per part of the parapet should be too much weakened. This is, indeed, double of what is allowed in permanent fortification. If the plonge cannot be directed to the crest of the counterscarpe, it will be proper to construct a glacis, having the same slope as the plonge of the parapet. It is to be particularly observed, however, that if a place can be cannonaded by the enemy, the slope is to be reduced as much as possible.
The thickness of a parapet depends on the purpose for which it is intended, and the ordnance that may be brought against it. If it is only a temporary place of security, till reinforcements come up, two to four feet in thickness will be sufficient, as it will, in all probability, be attacked by small arms alone. I3ut if great guns are likely to be em ployed by the enemy, or if the work is to continue for any considerable time, the parapet ought to be at least 10 feet. A four pounder ball enters about 4 feet, an eight pounder 6 feet, and a twelve pounder about 8 feet in common earth, such as is generally used in constructing fortifications. If therefore a heavy cannonade be expected, the parapet will require to be 12 feet, or perhaps in some cases more.