152 MILITARY SCIENCES. 



redoubts; and these likewise may be either inclosed or open redoubts. 

 They must always be large enough to contain two thirds of the garrison, 

 and their form is governed by that of the main work. In inclosed works 

 the redoubts are so placed {fig. 25) that their fire will principally sweep the 

 dead-angles of the main work, as upon these points, which have only a 

 secondary defence, the attack is chiefly directed. In open works, those 

 especially which are so frequently thrown up to cover the passage of a river, 

 the redoubts {fig. 26) are also constructed with fixed parapets, according to 

 the importance of the main work ; and a second redoubt, of palisades, is in 

 such cases often added. If the works are less permanently constructed, the 

 redoubts are made only of palisades {fig. 27), or of felled trees (abattis), or 

 the so-called Spanish riders (chevaux de frise, fig. 28), beams, through 

 which, in all directions, long stakes shod with iron at the points are thrust. 

 To obtain in permanent works a better defence for the ditch, a subterranean 

 block-house {fig. 47) is constructed in the counterscarp of the salients, 

 under the parapet/e d {fig. 46, F, section, and fig. 47 view), into which is 

 a subterranean entrance from D, by the gallery G. X Y is the line of the 

 horizon, b a the prolongation of the superior slope of the parapet. In slight 

 works, a ditch-defence is obtained by setting the palisades w {fig. 23) a 

 small distance from the scarp, and arranging them with loopholes. 



f. Defensive Means which are Part of the Works themselves. The 

 covered way is the space dd from the edge of the counterscarp {pi. 47, fig. 

 36, front K K) to the breastwork which is thrown up in the open field, and 

 affords a low defence. This construction is found only in large forts ; for 

 small ones only a simple embankment is thrown up, the glacis w w {fig. 36, 

 front H H). The covered way is from eight to ten feet in width. To pro- 

 tect the garrison from being taken in flank by the fire of the enemy (enfi- 

 laded), cross-dikes (traverses) are thrown up on the long lines u u {fig. 36 

 front L L). To strengthen the covered way, places of arms are established 

 in the re-entering angles d d and h ; in the salients they are found ready 

 formed 2Xdd and v ; they must also be covered by traverses. The traverses 

 lie close to the counterscarp, and are notched in the parapet of the covered 

 way for the passage around them. Even where there is only a glacis places 

 of arms are sometimes established in the re-entering angles q q {fig. 36, 

 front H H) ; these serve, however, principally as mustering places for sal- 

 lies, and are sunk in the natural earth. If it is desired to strengthen the 

 defence still more, a second glacis is thrown up, xx {fig. 36, G X), which, 

 however, must be commanded by the first, and therefore renders a higher 

 parapet necessary. 



Where it is possible the ditches should be provided with water, which, 

 when the ground is swampy, is carried to its place by collecting ditches. 

 At the foot of the glacis and in the dry ditches trous de hup are dug, holes 

 of eight to ten feet deep, running down to a point, in which a sharp stake 

 is set. Palisades, also, and abattis are good defences at the foot of the 

 glacis and in the dry ditches, as they detain the assailants within the range 

 of fire. The chevaux de frise, already mentioned in treating of redoubts, 

 caltrops, and small thickly set stakes, driven firmly into the ground upon the 

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