On War

by Carl von Clausewitz

The offensive had thus again gained a preponderance through the greater mobility of troops; and it was only through the same means that the defence could seek for help. But mountainous ground by its nature is opposed to mobility, and thus the whole theory of mountain defence experienced, if we may use the expression, a defeat like that which the armies engaged in it in the Revolutionary war so often suffered.

But that we may not reject the good with the bad, and allow ourselves to be carried along by the stream of commonplace to assertions which, in actual experience, would be refuted a thousand times by the force of circumstances, we must distinguish the effects of mountain defence according to the nature of the cases.

The principal question to be decided here, and that which throws the greatest light over the whole subject is, whether the resistance which is intended by the defence of mountains is to be relative or absolute—whether it is only intended to last for a time, or is meant to end in a decisive victory. For a resistance of the first kind mountainous ground is in a high degree suitable, and introduces into it a very powerful element of strength; for one of the latter kind, on the contrary, it is in general not at all suitable, or only so in some special cases.

In mountains every movement is slower and more difficult, costs also more time, and more men as well, if within the sphere of danger. But the loss of the assailant in time and men is the standard by which the defensive resistance is measured. As long as the movement is all on the side of the offensive so long the defensive has a marked advantage; but as soon as the defensive resorts to this principle of movement also, that advantage ceases. Now from the nature of the thing, that is to say, on tactical grounds, a relative resistance allows of a much greater degree of passivity than one which is intended to lead to a decisive result, and it allows this passivity to be carried to an extreme, that is, to the end of the combat, which in the other case can never happen. The impeding element of mountain ground, which as a medium of greater density weakens all positive activity, is, therefore, completely suited to the passive defence.

We have already said that a small post acquires an extraordinary strength by the nature of the ground; but although this tactical result in general requires no further proof, we must add to what we have said some explanation. We must be careful here to draw a distinction between what is relatively and what is absolutely small. If a body of troops, let its size be what it may, isolates a portion of itself in a position, this portion may possibly be exposed to the attack of the whole body of the enemy’s troops, therefore of a superior force, in opposition to which it is itself small. There, as a rule, no absolute but only a relative defence can be the object. The smaller the post in relation to the whole body from which it is detached and in relation to the whole body of the enemy, the more this applies.

But a post also which is small in an absolute sense, that is, one which is not opposed by an enemy superior to itself, and which, therefore, may aspire to an absolute defence, a real victory, will be infinitely better off in mountains than a large army, and can derive more advantage from the ground as we shall show further on.

Our conclusion, therefore, is, that a small post in mountains possesses great strength. How this may be of decisive utility in all cases which depend entirely on a relative defence is plain of itself; but will it be of the same decisive utility for the absolute defence by a whole army? This is the question which we now propose to examine.

First of all we ask whether a front line composed of several posts has, as has hitherto been assumed, the same strength proportionally as each post singly. This is certainly not the case, and to suppose so would involve one of two errors.

In the first place, a country without roads is often confounded with one which is quite impassable. Where a column, or where artillery and cavalry cannot march, infantry may still, in general, be able to pass, and even artillery may often be brought there as well, for the movements made in a battle by excessive efforts of short duration are not to be judged of by the same scale as marches. The secure connection of the single posts with one another rests therefore on an illusion, and the flanks are in reality in danger.

Or next it is supposed, a line of small posts, which are very strong in front, are also equally strong on their flanks, because a ravine, a precipice, etc., etc., form excellent supports for a small post. But why are they so?—not because they make it impossible to turn the post, but because they cause the enemy an expenditure of time and of force, which gives scope for the effectual action of the post. The enemy who, in spite of the difficulty of the ground, wishes, and in fact is obliged, to turn such a post, because the front is unassailable requires, perhaps, half-a-day to execute his purpose, and cannot after all accomplish it without some loss of men. Now if such a post can be succoured, or if it is only designed to resist for a certain space of time, or lastly, if it is able to cope with the enemy, then the flank supports have done their part, and we may say the position had not only a strong front, but strong flanks as well. But it is not the same if it is a question of a line of posts, forming part of an extended mountain position. None of these three conditions are realised in that case. The enemy attacks one point with an overwhelming force, the support in rear is perhaps slight, and yet it is a question of absolute resistance. Under such circumstances the flank supports of such posts are worth nothing.