Elements of Military Art and Science / Or, Course Of Instruction In Strategy, Fortification, Tactics Of Battles, &C.; Embracing The Duties Of Staff, Infantry, Cavalry, Artillery, And Engineers; Adapted To The Use Of Volunteers And Militia; Third Edition; With Critical Notes On The Mexican And Crimean Wars.

by H. W. Halleck

The work by which the space fortified is immediately enveloped, is called the enceinte, or body of the place. Other works are usually added to the enceinte to strengthen the weak points of the fortification, or to lengthen the siege by forcing the enemy to gain possession of them before he can breach the body of the place: these are termed outworks, when enveloped by the covered way, and advanced works, when placed exterior to the covered way, but in some way connected with the main work; but if entirely beyond the glacis, and not within supporting distance of the fortress, they are called detached works.

In a bastioned front the principal outwork is the demi-lune, which is placed in front of the curtain; it serves to cover the main entrance to the work, and to place the adjacent bastions in strong re-enterings.

The tenaille is a small low work placed in the ditch, to cover the scarp wall of the curtain and flanks from the fire of the besieger's batteries erected along the crest of the glacis.

The places of arms, are points where troops are assembled in order to act on the exterior of the work. The re-entering places of arms, are small redans arranged at the points of junction of the covered ways of the bastion and demi-lune. The salient places of arms are the parts of the covered way in front of the salients of the bastion and demi-lune.

Small permanent works, termed redoubts, are placed within the demi-lune and re-entering places of arms for strengthening those works. Works of this character constructed within the bastion are termed interior retrenchments; when sufficiently elevated to command the exterior ground, they are called cavaliers.

Caponniers are works constructed to cover the passage of the ditch from the tenaille to the gorge of the demi-lune, and also from the demi-lune to the covered way, by which communication may be maintained between the enceinte and outworks.

Posterns are underground communications made through the body of the place or some of the outworks.

Sortie-passages are narrow openings made through the crest of the glacis, which usually rise in the form of a ramp from the covered way, by means of which communication may be kept up with the exterior. These passages are so arranged that they cannot be swept by the fire of the enemy. The other communications above ground are called ramps, stairs, &c.

Traverses are small works erected on the covered way to intercept the fire of the besieger's batteries.

Scarp and counterscarp galleries are sometimes constructed for the defence of the ditch. They are arranged with loop-holes, through which the troops of the garrison fire on the besiegers when they have entered the ditch, without being themselves exposed to the batteries of the enemy.