Front Page Titles (by Subject) CHAPTER XI: FORTRESSES ( Continued ) - On War, vol. 2
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CHAPTER XI: FORTRESSES ( Continued ) - Carl von Clausewitz, On War, vol. 2 
On War, trans. Col. J.J. Graham. New and Revised edition with Introduction and Notes by Col. F.N. Maude, in Three Volumes (London: Kegan Paul, Trench, Trubner & C., 1918). Vol. 2.
Part of: On War
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We have discussed the object of fortresses: now for their situation. At first the subject seems very complicated, when we think of the diversity of objects, each of which may again be modified by the locality; but such a view has very little foundation if we keep to the essence of the thing, and guard against unnecessary subtilties.
It is evident that all these demands are at once satisfied, if, in those districts of country which are to be regarded as the theatre of War, all the largest and richest towns on the great high roads connecting the two countries with each other are fortified, more particularly those adjacent to harbours and bays of the sea, or situated on large rivers and in mountains. Great towns and great roads always go hand in hand, and both have also a natural connection with great rivers and the coasts of the sea, all these four conditions, therefore, agree very well with each other, and give rise to no incongruity; on the other hand, it is not the same with mountains, for large towns are seldom found there. If, therefore, the position and direction of a mountain chain makes it favourable to a defensive line, it is necessary to close its roads and passes by small forts, built for this purpose only, and at the least possible cost, the great outlay on works of fortification being reserved for the important places of arms in the level country.
We have not yet noticed the frontiers of the state, nor said anything of the geometrical form of the whole system of fortresses, nor of the other geographical points in connection with their situation, because we regard the objects above mentioned as the most essential, and are of opinion that in many cases they alone are sufficient, particularly in small States. But, at the same time, other considerations may be admitted, and may be imperative in countries of a greater superficial extent, which either have a great many important towns and roads, or, on the contrary, are almost without any, which are either very rich, and, possessing already many fortresses, still want new ones, or those which, on the other hand, are very poor, and under the necessity of making a few answer, in short, in cases where the number of fortresses does not correspond with the number of important towns and roads which present themselves, being either considerably greater or less.
We shall now cast a glance at the nature of such other considerations.
The chief questions which remain relate to—
1. The choice of the principal roads, if the two countries are connected by more roads than we wish to fortify.
2. Whether the fortresses are to be placed on the frontier only, or spread over the country. Or,
3. Whether they shall be distributed uniformly, or in groups.
4. Circumstances relating to the geography of the country to which it is necessary to pay attention.
A number of other points with respect to the geometrical form of the line of fortifications, such as whether they should be placed in a single line or in several lines, that is, whether they do more service when placed one behind another, or side by side in line with each other; whether they should be chequer-wise, or in a straight line; or whether they should take the form of a fortification itself, with salients and re-entering angles—all these we look upon as empty subtilties, that is, considerations so insignificant, that, compared with the really important points, they are not worth notice; and we only mention them here because they are not merely treated of in many books, but also a great deal more is made of this rubbish than it is worth.
As regards the first question, in order to place it in a clearer light we shall merely instance the relation of the south of Germany to France, that is, to the upper Rhine. If, without reference to the number of separate States composing this district of country, we suppose it a whole which is to be fortified strategically, much doubt will arise, for a great number of very fine roads lead from the Rhine into the interior of Franconia, Bavaria, and Austria. Certainly, towns are not wanting which surpass others in size and importance, as Nuremburg, Wurzburg, Ulm, Augsburg, and Munich; but if we are not disposed to fortify all, there is no alternative but to make a selection. If, further, in accordance with our view, the fortification of the greatest and wealthiest is held to be the principal thing, still it is not to be denied that, owing to the distance between Nuremburg and Munich, the first has a very different strategic signification from the second; and therefore it always remains to be considered whether it would not be better, in place of Nuremburg, to fortify some other place in the neighbourhood of Munich, even if the place is one of less importance in itself.
As concerns the decision in such cases, that is, answering the first question, we must refer to what has been said in the chapters on the general plan of defence, and on the choice of points of attack. Wherever the most natural point of attack is situated, there the defensive arrangements should be made by preference.
Therefore, amongst a number of great roads leading from the enemy’s country into ours, we should first of all fortify that which leads most directly to the heart of our dominions, or that which, traversing fertile provinces, or running parallel to navigable rivers, facilitates the enemy’s undertaking, and then we may rest secure. The assailant then encounters these works, or should he resolve to pass them by, he will naturally offer a favourable opportunity for operations against his flank.
Vienna is the heart of South Germany, and plainly Munich or Augsburg, in relation to France alone (Switzerland and Italy being therefore supposed neutral) would be more efficient as a principal fortress than Nuremburg or Wurzburg. But if, at the same time, we look at the roads leading from Italy into Germany by Switzerland and the Tyrol, this will become still more evident, because, in relation to these, Munich and Augsburg will always be places of importance, whereas Wurzburg and Nuremburg are much the same, in this respect, as if they did not exist.
We turn now to the second question—Whether the fortresses should be placed on the frontier, or distributed over the country? In the first place, we must observe, that, as regards small States, this question is superfluous, for what are called strategic frontiers coincide, in their case, nearly with the whole country. The larger the State is supposed to be in the consideration of this question, the plainer appears the necessity for its being answered.
The most natural answer is,—that fortresses belong to the frontiers, for they are to defend the State, and the State is defended as long as the frontiers are defended. This argument may be valid in the abstract, but the following considerations will show that it is subject to very many modifications.
Every defence which is calculated chiefly on foreign assistance lays great value on gaining time: it is not a vigorous counterstroke, but a slow proceeding, in which the chief gain consists more in delay than in any weakening of the enemy which is effected. But now it lies in the nature of the thing that, supposing all other circumstances alike, fortresses which are spread over the whole country, and include between them a very considerable area of territory, will take longer to capture than those squeezed together in a close line on the frontier. Further, in all cases in which the object is to overcome the enemy through the length of his communications, and the difficulty of his existence, therefore in countries which can chiefly reckon on this kind of reaction, it would be a complete contradiction to have the defensive preparations of this kind only on the frontier. Lastly, let us also remember that, if circumstances will in any way allow of it, the fortification of the capital is a main point; that according to our principles the chief towns and places of commerce in the provinces demand it otherwise; that rivers passing through the country, mountains, and other irregular features of ground, afford advantages for new lines of defence; that many towns, through their strong natural situation, invite fortification; moreover, that certain accessories of War, such as manufactories of arms, &c., are better placed in the interior of the country than on the frontier, and their value well entitles them to the protection of works of fortification; then we see that there is always more or less occasion for the construction of fortresses in the interior of a country; on this account we are of opinion, that although States which possess a great number of fortresses are right in placing the greater number on the frontier, still it would be a great mistake if the interior of the country was left entirely destitute of them. We think that this mistake has been made in a remarkable degree in France.—A great doubt may with reason arise if the border provinces of a country contain no considerable towns, such towns lying further back towards the interior, as is the case in South Germany in particular, where Swabia is almost destitute of great towns, whilst Bavaria contains a large number. We do not hold it to be necessary to remove these doubts once for all on general grounds, believing that in such cases, in order to arrive at a solution, reasons derived from the particular situation must come into consideration. Still we must call attention to the closing remarks in this chapter.
The third question—Whether fortresses should be disposed in groups, or more equally distributed?—will, if we reflect upon it, seldom arise; still we must not, for that reason, set it down as a useless subtilty, because certainly a group of two, three, or four fortresses, which are only a few days’ march from a common centre, give that point and the Army placed there such strength, that, if other conditions allowed of it, in some measure one would be very much tempted to form such a strategic bastion.
The last point concerns the other geographical properties of the points to be chosen. That fortresses on the sea, on streams and great rivers, and in mountains, are doubly effective, has been already stated to be one of the principal considerations; but there are a number of other points in connection with fortresses to which regard must be paid.
If a fortress cannot lie on the river itself, it is better not to place it near, but at a distance of fifty to sixty miles from it; otherwise, the river intersects, and lowers the value of the sphere of action of the fortress in all those points above mentioned.*
This is not the same in mountains, because there the movement of large or small masses upon particular points is not restricted in the same degree as it is by a river. But fortresses on the enemy’s side of a mountain are not well placed, because they are difficult to succour. If they are on our side, the difficulty of laying siege to them is very great, as the mountains cut across the enemy’s line of communication. We give Olmütz, 1758, as an example.
It is easily seen that impassable forests and marshes have a similar effect to that of rivers.
The question has been often raised as to whether towns situated in a very difficult country are well or ill suited for fortresses. As they can be fortified and defended at a small expense, or be made much stronger, often impregnable, at an equal expenditure, and the services of a fortress are always more passive than active, it does not seem necessary to attach much importance to the objection that they can easily be blockaded.
If we now, in conclusion, cast a retrospective glance over our simple system of fortification for a country, we may assert that it rests on comprehensive data, lasting in their nature, and directly connected with the foundations of the state itself, not on transient views on War, fashionable only for a day; not on imaginary strategic niceties, nor on requirements completely singular in character—an error which might be attended with irreparable consequences if allowed to influence the construction of fortresses intended to last five hundred, perhaps a thousand, years. Silberberg, in Silesia, built by Frederick the Great on one of the ridges of the Sudetics, has, from the complete alteration in circumstances which has since taken place, lost almost entirely its importance and object, whilst Breslau, if it had been made a strong place of arms, and continued to be so, would have always maintained its value against the French, as well as against the Russians, Poles, and Austrians.
Our reader will not overlook the fact that these considerations are not raised on the supposed case of a State providing itself with a set of new fortifications; they would be useless if such was their object, as such a case seldom, if ever, happens; but they may all arise at the designing of each single fortification.
[* ]Philippsburg was the pattern of a badly-placed fortress; it resembled a fool standing with his nose close to a wall.