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 likewise; 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 ten or twelve 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.(*)
(*) Philippsburg was the pattern of a badly-placed fortress; it resembled a fool standing with his nose close to a wall.
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.