What is "tenaille"

Tenaille \Te*naille"\, n. [F., a pair of pincers or tongs, a tenaille, fr. L. tenaculum. See Tenaculum.] (Fort.) An outwork in the main ditch, in front of the curtain, between two bastions. See Illust. of Ravelin.

n. (context military historical English) An outwork in the main ditch of a fortification, in front of the curtain, between two bastions.

Tenaille (archaic Tenalia) is an advanced defensive-work, in front of the main defences of a fortress which takes its name from resemblance, real or imaginary, to the lip of a pair of pincers. It is "from French, literally: tongs, from Late Latin tenācula, pl of tenaculum".

In a letter to John Bradshaw, President of the Council of State in London, Oliver Cromwell writing from Dublin on 16 September 1649 described one such tenaille that played a significant part during the storming of Drogheda.

Tenaille were a development in fortification formalised by Vauban, among others. To allow the defenders to access the ditches that front a curtain wall a postern gate was placed low down in the wall close to its centre. To protect the postern, an outwork, originally vee-shaped, was placed in front of the gate, providing an area where the defenders could leave the fortification without being seen or directly shot at. A simple tenaille is shown in the top image to the right; it is the chevron between the two corner bastions.

The design also evolved a version in which the tenaille possess projections at each end, as seen in the middle image right.

Finally, the word was also used for some other vee-shaped parts of outworks; the bottom-most image, a priest's cap, has two tenailles.

Also shown is another approach to protect a gate; the roughly triangular outwork seen in the middle of the bottom drawing is a ravelin.