Intrenched camps near the frontiers differ very much from permanent camps and frontier posts, having no habi tations for the troops in them, and being only intended to serve for a short time. They generally consist of works constructed like field fortifications ; but, that they may be tenable as long as possible, they ought to be situated be hind such places or parts of the ground as do not allow the enemy to approach.
Tetes-de-ponts, or bridge-heads, arc smaller or larger fortifications, raised before a bridge in order to cover it. Small tites-de-ponts consist only of a single redan, as ABC, Plate CCLVIII. Fig. 6, the sides of which are favourably flanked by two traverses D and E. Such ate's de-fionts are always to be constructed there, that the enemy may not attack them ; that the bridge which they cover may not be destroyed by him ; and that, while attacking, he may be taken in flank. These works frequently re quire a considerable space, either to ccntain divisions of an army retreating- by them, or to cover a large space of the river or its banks. Large tetes-delionts are represent ed in Fig. 7. and still larger in Fig. 8. Tetes-delionta must always be well enflanked towards the enemy by the other parts of the works, and ought. also to have a proper flanking fire of their own. The entrances to them should not be too small, to retard the movements of the troops ; but they should be well defended, so as to deter the enemy from approaching then).
An army which is weaker than that of its enemy, must sometimes either maintain its position, or secure its move meats by the aid of fortifications; and, in this case, whole lines, or...connecting works, are to be constructed, in which advantage is always to be taken of the natural impediments offered by the ground, so as to strengthen these works as much as circumstances will permit For the intrenchments of armies at present, unconnect ed lines or fortifications are always preferred ; but those which are connected, and which form whole lines, are also of use, where any place is to be covered by a connected line ; and, in this case, it is more advantageous than sepa rated works. The latter possess these advantages, how ever, that they allow the troops free movements ; they do not require so many men for their defence ; they cover the most essential points, and are constructed at less expenee.
Besides this, two lines, or even three, may be formed of them, and then they allow a stronger defence than con nected lines. The figure to be adopted in constructing lines, is that which admits most readily the use of all kinds of fire-arms. Different engineers have proposed different figures ; but what appears to us the most advantageous, is that represented in Plate CCLVIII. Fig. 9.
Detached works possess in many cases, as we have al ready said, great advantages over connected lines, and are in modern times generally preferred. Where a part of a country, however, has been completely inclosed by con nected lines, they are, besides having a good profile, made as strong by the impediments of the ground as circum stances will permit. Of detached works, three lines of re doubts are the most advantageous, as they are inclosed, and may be placed in such a manner that they defend each other as strongly as if they had flanks. Each of these re doubts is by itself a strong work ; but, when supported by the four neighbouring ones, it can never be taken but by attacking all the others. In such redoubts there should always be a considerable number of cavalry ready to attack the enemy whenever they are thrown into the least confu sion.
Fleches applied to this purpose can be taken in rear, if they are not shut ; and, even in this case, their garrisons are more exposed, and the enemy may always attack them from behind. It is the same with bastions, though these certainly have a stronger and better defence than fleches, and consequently are preferable. However, their gorges should always be shut, that they may not be taken in rear. The spaces among the detached works are, if possible, made impracticable, and only a few large passages are left open, through which the troops may with ease advance upon the enemy. The first line of such detached works is always to be the strongest, though the great gulls should be placed in the second and third lines, that the enemy, after taking the first, may not get the advantage of them in attacking the other lines.