Embrasures may be made either direct or oblique, according as the fire is required to be perpendicular or oblique to the parapet.
A _coverport_ is a small outwork of any convenient form, erected immediately in front of a gateway, to screen it from the enemy's fire.
A _counterguard_ is a more extensive work, constructed in front of a part of the fortress itself, or of some other outwork of greater importance, which it is intended to cover.

These are sometimes called _coverfaces_, from their situation and object; but the former term is most commonly used.
Sometimes outworks, called _tenaillons_, consisting of one long and one short face, are placed on each side of the demi-lune of a front of fortification, for the purpose of prolonging the siege.

(Fig.

41.) Small, or _demi_-tenaillons, are frequently so arranged as to cover only one-half of the demi-lune, and then a _bonnet_ constructed in front of the salient of the demi-lune.

(Fig.42.) In this case the bonnet is flanked by the short faces of the demi-tenaillons; these short faces are themselves flanked by the demi-lune, while the bastions flank the long faces.
A _horn-work_ consists of a front of fortification, and two wings resting on the faces of bastions of a front of the fortress.