2. Facility of providing shelter for the troops. 3. Security of the rear. 4. An open country in front. 5. The position itself in a broken country. 6. Strategic points d’appui. 7. A suitable distribution of the troops. Our elucidation of these several points is as follows: The first two lead us to seek out cultivated districts, and great towns and roads. They determine measures in general rather than in particular. In the chapter on lines of communication will be found what we mean by security of the rear. The first and most important point in this respect is that the centre of the position should be at a right angle with the principal line of retreat adjoining the position. Respecting the fourth point, an army certainly cannot look over an expanse of country in its front as it overlooks the space directly before it when in a tactical position for battle. But the strategic eyes are the advanced guard, scouts and patrols sent forward, spies, etc., etc., and the service will naturally be easier for these in an open than in an intersected country. The fifth point is merely the reverse of the fourth. Strategical points d’appui differ from tactical in these two respects, that the army need not be in immediate contact with them, and that, on the other hand, they must be of greater extent. The cause of this is that, according to the nature of the thing, the relations to time and space in which strategy moves are generally on a greater scale than those of tactics. If, therefore, an army posts itself at a distance of a mile from the sea coast or the banks of a great river, it leans strategically on these obstacles, for the enemy cannot make use of such a space as this to effect a strategic turning movement. Within its narrow limits he cannot adventure on marches miles in length, occupying days and weeks. On the other hand, in strategy, a lake of several miles in circumference is hardly to be looked upon as an obstacle; in its proceedings, a few miles to the right or left are not of much consequence. Fortresses will become strategic points d’appui, according as they are large, and afford a wide sphere of action for offensive combinations. The disposition of the army in separate masses may be done with a view either to special objects and requirements, or to those of a general nature; here we can only speak of the latter. The first general necessity is to push forward the advanced guard and the other troops required to watch the enemy. The second is that, with very large armies, the reserves are usually placed several miles in rear, and consequently occupy a separate position. Lastly, the covering of both wings of an army usually requires a separate disposition of particular corps.