The consequence is, that enterprises of this description on a flank, which have always been more in fashion in books than in real warfare, now appear less of a practical nature than ever, and we may safely say that there is no danger in this respect to any lines of communication but such as are very long, and otherwise unfavourably circumstanced, more especially by being exposed everywhere and at any moment to attacks from an _insurgent population_. With respect to the cutting off an enemy’s retreat, we must not be overconfident in this respect either of the consequences of threatening or closing the enemy’s lines of retreat, as recent experience has shown that, when troops are good and their leader resolute, it is _more difficult_ to make them prisoners, than it is for them to cut their way through the force opposed to them. The means of shortening and protecting long lines of communication are very limited. The seizure of some fortresses adjacent to the position taken up by the army, and on the roads leading to the rear—or in the event of there being no fortresses in the country, the construction of temporary defences at suitable points—the kind treatment of the people of the country, strict discipline on the military roads, good police, and active measures to improve the roads, are the only means by which the evil may be diminished, but it is one which can never be entirely removed. Furthermore, what we said when treating of the question of subsistence with respect to the roads which the army should chose by preference, applies also particularly to lines of communication. The best lines of communication are roads leading through the most flourishing towns and the most important provinces; they ought to be preferred, even if considerably longer, and in most cases they exercise an important influence on the definitive disposition of the army. CHAPTER XVII. On Country and Ground Quite irrespective of their influence as regards the means of subsistence of an army, country and ground bear another most intimate and never-failing relation to the business of war, which is their decisive influence on the battle, both upon what concerns its course, as well as upon the preparation for it, and the use to be made of it. We now proceed to consider country and ground in this phase, that is, in the full meaning of the French expression “_Terrain._” The way to make use of them is a subject which lies mostly within the province of tactics, but the effects resulting from them appear in strategy; a battle in the mountains is, in its consequences as well as in itself, quite a different thing from a battle on a level plain.