A tenaillon is a kind of couvre face A, Plate CCLVII. Fig. 4. constructed on each side of a small ravelin B, to inct ease its strength, and cover the shoulder of the bastion. To trace a tenaillon, produce the face of the ravelin, and, leaving from 60 to 80 feet for the fos-e, set off a b equal to 180 feet. On the counterscarpe of the bastion, set off c d equal to 90 feet, and a b d c will be the tenaillom Works of this kind are sometimes a little different from that re presented in Fig. 4. But it may be remarked of all of them, that they are much inferior to large ravelins. They are in consequence very seldom adopted.
Counterguards are works placed sometimes before the bastion, and sometimes before the ravelin ; but the latter position is now generally preferred, as they thereby answer the purpose of large demi-Miles. A counterguard before the ravelin is represented in Plate CCLVIII. Fig. 1. where AB is equal to about 240 feet, and CD about 60. A coon terguard before the bastion does not afford sufficient pro tection to the shoulder, and is, besides, one third more ex pensive than that before the ravelin. At the same time, it may be of essential service in that position, especially if the revetement of the bastion be very high compared with the covered way. Counterguards should have a revete ment all around, as high as the terre-plein, with a fosEe from 70 to 90 feet wide. It will also increase the strength of the work, to have a coupure a b before its reduit, with a fosse 20 to 24 feet wide, lined on both sides with a reve temem up to the terre-plein. Under the parapet of the coupure is a postern, with stairs to communicate with the counterguard. The ditch of the coupure ought not to be so cheep as the large ditch by six feet, if both are dry ; but if the great ditch be wet, the bottom of Lie small ditch will not require to be more than one foot above the highest wa ter. The revetement, from the bottom of the ditch of the coupure, ought to be at least 10 feet high, to prevent a sur prise in case the enemy should get possession of the place of arms E. Coupures in general should be perpendicular to the faces, and so laid as that the enemy cannot batter them from the covered way. They should also be placed near the extremity of the ten e-pleio FG towards the en ceinte, that the communication with the latter may be the better secured.
When there is a scarcity of earth, a ditch is sometimes constructed before the covered way, or rather beim e the glacis, called the avantfusse. it is not, however, of much use, unless it can be made wet and dry at pleasure, and is rather incommodious to the soldiers when making a sally, The avant-covered-way is a second covered way before the first or before the avant-fosse ; but is useful only in large fortresses, which have numerous garrisons. It is constructed in the same way as the first, care being taken that the tire of the latter is not interrupted by the former. The avant-covered-way communicates with the works be hind by means of bridges or caponniers, the inner extremi ty of which terminates in the places of arms.
Fleshes are works of two lines of faces, forming an an gle, and generally constructed over saliant angles. 'they are sometimes useful in covering a passage, but In general they are incapable of making any resistance.
Lunettes are works resembling ravelins, but consisting only of a parapet, placed opposite the saliant angle of the covered way, as H and K, Plate CCLVIII. Fig. 1. If the covered-way has an avant-fosse, the lunettes are placed in the fosse ; but if it has none, they are constructed at the foot of the glacis, as H and K, Pig. I. When surrounded by a ditch and covered-way, they form an excellent de fence ; and, by obliging the enemy to open his works at a greater distance from the place, they essentially prolong the siege. They are also useful in sorties.
Lunettes ought not to be placed too far from the en ceinte ; their angles should be at least 60 degrees, that it may be defended by guns ; and the faces from 100 to 200 feet long. They are always of the greatest advantage, when the angles of the bastions arc very open. The most advantageous arrangement of lunettes, and that by which they best defend one another, is where the straight lines joining joining them make saliant and re-entering angles alternate ly; the saliant before the ravelin, and the re-entering be fore the bastion. In this way, too, the greatest number can be made to defend one bastion, all which must be taken before the bastion itself be assaulted. Flanks of from 50 to 60 feet are necessary in lunettes. The angles of these flanks increase as that of the bastion diminishes, and vice versa.