On War

by Carl von Clausewitz

Merely by entrenchments alone they can hardly be formed, except as entrenched camps resting on fortresses; but still less are they to be found ready formed entirely by natural obstacles. Art usually lends a hand to assist nature, and therefore they are frequently designated as entrenched camps or positions. At the same time, that term may really be applied to any position strengthened more or less by field works, which need have nothing in common with the nature of the position we are now considering.

The object of a strong position is to make the force there stationed in point of fact unattackable, and by that means, either really to cover a certain space directly, or only the troops which occupy that space in order then, through them, in another way to effect the covering of the country indirectly. The first was the signification of the lines of former times, for instance, those on the French frontier; the latter, is that of entrenched camps laid out near fortresses, and showing a front in every direction.

If, for instance, the front of a position is so strong by works and hindrances to approach that an attack is impossible, then the enemy is compelled to turn it, to make his attack on a side of it or in rear. Now to prevent this being easily done, points d’appui were sought for these lines, which should give them a certain degree of support on the side, such as the Rhine and the Vosges give the lines in Alsace. The longer the front of such a line the more easily it can be protected from being turned, because every movement to turn it is attended with danger to the side attempting the movement, the danger increasing in proportion as the required movement causes a greater deviation from the normal direction of the attacking force. Therefore, a considerable length of front, which can be made unassailable, and good flank-supports, ensure the possibility of protecting a large space of territory directly from hostile invasion: at least, that was the view in which works of this class originated; that was the object of the lines in Alsace, with their right flank on the Rhine and the left on the Vosges; and the lines in Flanders, fifteen miles long, resting their right on the Scheldt and the fortress of Tournay, their left on the sea.

But when we have not the advantages of such a long well-defended front, and good flank-supports, if the country is to be held generally by a force well entrenched, then that force (and its position) must be protected against being turned by such an arrangement that it can show a front in every direction. But then the idea of a thoroughly covered tract of country vanishes, for such a position is only strategically a point which covers the force occupying it, and thus secures to that force the power of keeping the field, that is to say, maintaining itself in the country. Such a camp cannot be turned, that is, cannot be attacked in flank or rear by reason of those parts being weaker than its front, for it can show front in all directions, and is equally strong everywhere. But such a camp can be passed by, and that much easier than a fortified line, because its extent amounts to nothing.

Entrenched camps connected with fortresses are in reality of this second kind, for the object of them is to protect the troops assembled in them; but their further strategic meaning, that is, the application of this protected force, is somewhat different from that of other fortified camps.

Having given this explanation of the origin of these three different defensive means, we shall now proceed to consider the value of each of them separately, under the heads of strong lines, strong positions, and entrenched camps resting on fortresses.

1. Lines.—They are the worst kind of cordon war: the obstacle which they present to the aggressor is of no value at all unless they are defended by a powerful fire; in themselves they are simply worthless. But now the extent to which an army can furnish an effective fire is generally very small in proportion to the extent of country to be defended; the lines can, therefore, only be short, and consequently cover only a small extent of country, or the army will not be able really to defend the lines at all points. In consequence of this, the idea was started of not occupying all points in the line, but only watching them, and defending them by means of strong reserves, in the same way as a small river may be defended; but this procedure is in opposition to the nature of the means. If the natural obstacles of the ground are so great that such a method of defence could be applied, then the entrenchments were needless, and entail danger, for that method of defence is not local, and entrenchments are only suited to a strictly local defence; but if the entrenchments themselves are to be considered the chief impediments to approach, then we may easily conceive that an undefended line will not have much to say as an obstacle to approach. What is a twelve or fifteen feet ditch, and a rampart ten or twelve feet high, against the united efforts of many thousands, if these efforts are not hindered by the fire of an enemy? The consequence, therefore, is, that if such lines are short and tolerably well defended by troops, they can be turned; but if they are extensive, and not sufficiently occupied, they can be attacked in front, and taken without much difficulty.

Now as lines of this description tie the troops down to a local defence, and take away from them all mobility, they are a bad and senseless means to use against an enterprising enemy. If we find them long retained in modern wars in spite of these objections, the cause lies entirely in the low degree of energy impressed on the conduct of war, one consequence of which was, that seeming difficulties often effected quite as much as real ones. Besides, in most campaigns these lines were used merely for a secondary defence against irregular incursions; if they have been found not wholly inefficacious for that purpose, we must only keep in view, at the same time, how much more usefully the troops required for their defence might have been employed at other points. In the latest wars such lines have been out of the question, neither do we find any trace of them; and it is doubtful if they will ever re-appear.

2. Positions.—The defence of a tract of country continues (as we shall show more plainly in the 27th chapter) as long as the force designated for it maintains itself there, and only ceases if that force removes and abandons it.

If a force is to maintain itself in any district of country which is attacked by very superior forces, the means of protecting this force against the power of the sword by a position which is unassailable is a first consideration.