3. Mountains considered in their aspect of a strategic barrier.
We must divide this subject under two heads.
The first is again that of a decisive battle. We can, for instance, consider the mountain chain as a river, that is, as a barrier with certain points of passage, which may afford us an opportunity of gaining a victory, because the enemy will be compelled by it to divide his forces in advancing, and is tied down to certain roads, which will enable us with our forces concentrated behind the mountains to fall upon fractions of his force. As the assailant on his march through the mountains, irrespective of all other considerations, cannot march in a single column because he would thus expose himself to the danger of getting engaged in a decisive battle with only one line of retreat, therefore, the defensive method recommends itself certainly on substantial grounds. But as the conception of mountains and their outlets is very undefined, the question of adopting this plan depends entirely on the nature of the country itself, and it can only be pointed out as possible whilst it must also be considered as attended with two disadvantages, the first is, that if the enemy receives a severe blow, he soon finds shelter in the mountains; the second is, that he is in possession of the higher ground, which, although not decisive, must still always be regarded as a disadvantage for the pursuer.
We know of no battle given under such circumstances unless the battle with Alvinzi in 1796 can be so classed. But that the case may occur is plain from Buonaparte’s passage of the Alps in the year 1800, when Melas might and should have fallen on him with his whole force before he had united his columns.
The second influence which mountains may have as a barrier is that which they have upon the lines of communication if they cross those lines. Without taking into account what may be done by erecting forts at the points of passage and by arming the people, the bad roads in mountains at certain seasons of the year may of themselves alone prove at once destructive to an army; they have frequently compelled a retreat after having first sucked all the marrow and blood out of the army. If, in addition, troops of active partisans hover round, or there is a national rising to add to the difficulties, then the enemy’s army is obliged to make large detachments, and at last driven to form strong posts in the mountains and thus gets engaged in one of the most disadvantageous situations that can be in an offensive war.