TENAILLE

, in Fortification, a kind of outwork, consisting of two parallel sides, with a front, having a re-entering angle. In fact, that angle, and the faces which compose it, are the Tenaille.

The Tenaille is of two kinds, simple and double.

Simple or Single Tenaille, is a large outwork, consisting of two faces or sides, including a re-entering angle.

Double, or Flanked Tenaille, is a large outwork, consisting of two simple Tenailles, or three saliant and two re-entering angles.

The great defects of Tenailles are, that they take up too much room, and on that account are advantageous to the enemy; that the re-entering angle is not defended; the height of the parapet preventing the seeing down into it, so that the enemy can lodge there under cover; and the sides are not sufficiently flanked. For these reasons, Tenailles are now mostly excluded out of fortification by the best engineers, and never made but where time does not serve to form a hornwork.

Tenaille of the Place, is the front of the place, comprehended between the points of two neighbouring bastions; including the curtain, the two flanks raised on the curtain, and the two sides of the bastions which face one another. So that the Tenaille, in this sense, is the same with what is otherwise called the face of a fortress.

Tenaille of the Ditch, is a low work raised before the curtain, in the middle of the foss or ditch; the parapet of which is only 2 or 3 feet higher than the level ground of the ravelin.

The use of Tenailles in general, is to defend the bottom of the ditch by a grazing fire, and likewise the level ground of the ravelin, which cannot be so conveniently defended from any other place. The first sort do not defend the ditch so well as the others, because they are too oblique a defence; but as they are not subject to be enfiladed, Vauban has generally preferred them in the fortifying of places. Those of the second sort defend the ditch much better than the first, and add a low flank to those of the bastions; but as these flanks are liable to be enfiladed, they have not been much used. This defect however might be remedied, by making them so as to be covered by the extremities of the parapets of the opposite ravelins, or by some other work. And the same thing may be said of the third sort as of the second.

The Ram's-horn is a curved Tenaille, raised in the foss before the flanks, and presenting its convexity to | the covered way. This work seems preferable to either of the other Tenailles, both on account of its simplicity, and the defence for which it is constructed.