On War

by Carl von Clausewitz

(b) That the means of taking it are at hand. Small means are only sufficient to take small places; but it is better to take a small one than to fail before a large one.

(c) Its strength in engineering respects, which obviously is not always in proportion to its importance in other respects. Nothing is more absurd than to waste forces before a very strong place of little importance, if a place of less strength may be made the object of attack.

(d) The strength of the armament and of the garrison as well. If a fortress is weakly armed and insufficiently garrisoned, its capture must naturally be easier; but here we must observe that the strength of the garrison and armament, are to be reckoned amongst those things which make up the total importance of the place, because garrison and armaments are directly parts of the enemy’s military strength, which cannot be said in the same measure of works of fortification. The conquest of a fortress with a strong garrison can, therefore, much more readily repay the sacrifice it costs than one with very strong works.

(e) The facility of moving the siege train. Most sieges fail for want of means, and the means are generally wanting from the difficulty attending their transport. Eugene’s siege of Landreci, 1712, and Frederick the Great’s siege of Olmütz, 1758, are very remarkable instances in point.

(f) Lastly, there remains the facility of covering the siege as a point now to be considered.

There are two essentially different ways by which a siege may be covered: by entrenching the besieging force, that is, by a line of circumvallation, and by what is called lines of observation. The first of these methods has gone quite out of fashion, although evidently one important point speaks in its favour, namely, that by this method the force of the assailant does not suffer by division exactly that weakening which is so generally found a great disadvantage at sieges. But we grant there is still a weakening in another way, to a very considerable degree, because—

1. The position round the fortress, as a rule, is of too great extent for the strength of the army.

2. The garrison, the strength of which, added to that of the relieving army, would only make up the force originally opposed to us, under these circumstances is to be looked upon as an enemy’s corps in the middle of our camp, which, protected by its walls, is invulnerable, or at least not to be overpowered, by which its power is immensely increased.

3. The defence of a line of circumvallation admits of nothing but the most absolute defensive, because the circular order, facing outwards, is the weakest and most disadvantageous of all possible orders of battle, and is particularly unfavourable to any advantageous counter-attacks. There is no alternative, in fact, but to defend ourselves to the last extremity within the entrenchments. That these circumstances may cause a greater diminution of the army than one-third which, perhaps, would be occasioned by forming an army of observation, is easy to conceive. If, added to that, we now think of the general preference which has existed since the time of Frederick the Great for the offensive, as it is called, (but which, in reality, is not always so) for movements and manœuvres, and the aversion to entrenchments, we shall not wonder at lines of circumvallation having gone quite out of fashion. But this weakening of the tactical resistance is by no means its only disadvantage; and we have only reckoned up the prejudices which forced themselves into the judgment on the lines of circumvallation next in order after that disadvantage, because they are nearly akin to each other. A line of circumvallation only in reality covers that portion of the theatre of war which it actually encloses; all the rest is more or less given up to the enemy if special detachments are not made use of to cover it, in which way the very partition of force which it was intended to obviate takes place. Thus the besieging army will be always in anxiety and embarrassment on account of the convoys which it requires, and the covering the same by lines of circumvallation, is not to be thought of if the army and the siege supplies required are considerable, and the enemy is in the field in strong force, unless under such conditions as are found in the Netherlands, where there is a whole system of fortresses lying close to each other, and intermediate lines connecting them, which cover the rest of the theatre of war, and considerably shorten the lines by which transport can be affected. In the time of Louis the Fourteenth the conception of a theatre of war had not yet bound itself up with the position of an army. In the Thirty Years’ War particularly, the armies moved here and there sporadically before this or that fortress, in the neighbourhood of which there was no enemy’s corps at all, and besieged it as long as the siege equipment they had brought with them lasted, and until an enemy’s army approached to relieve the place. Then lines of circumvallation had their foundation in the nature of circumstances.

In future it is not likely they will be often used again, unless where the enemy in the field is very weak, or the conception of the theatre of war vanishes before that of the siege. Then it will be natural to keep all the forces united in the siege, as a siege by that means unquestionably gains in energy in a high degree.