For a defensive position on high ground, it was usually laid down until the South African War that a line of trenches should be on the "military crest" (Fr. _crete militaire_), _i.e._ the highest point on the hill from which the whole of the slopes in front can be seen. Thus in the three sections of ground shown in fig. 79 it would be at a, b and c respectively. The simplicity of this prescription made it attractive and it came to be rather abused in the text-books. There were, even before the improvements in artillery, objections to it, because on most slopes the military crest would be found at very different elevations on different parts of the line, so that by a strict adherence to the rule some of the trenches would be placed near the top of the hill, and some in dangerous isolation near the bottom. Moreover a rounded hill has no military crest. [Illustration: FIG. 79.] Further, we have to consider nowadays not only the position of the fire-trenches, but those of supports, reserves and artillery, and the whole question is extremely difficult. For instance, considering the sections alone, as if they did not vary along the line, the positions at _a_ and _b_, fig. 79, are bad because they are on the sky-line and therefore a good mark for artillery. That at _b_ is especially bad because the slope in front is so steep that the defenders would have to expose themselves very much to fire down it, and the artillery fire against them can be kept up until the very last moment. The position _c_ has the advantage of not being on the sky-line, but the position of the supports in rear is exposed. [Illustration: FIG. 80.] Such a position as that at _d_, fig. 80, is good, but protected or concealed communications must be made for the supports coming from _e_ over the brow of the hill. [Illustration: FIG. 81.] Another possible position for the infantry line is at _f_, fig. 81, with the guns on the high ground behind. They might easily be quite concealed from the enemy's artillery. The drawback is that no retirement up the exposed slope would be possible for them, except at night. The fire from _f_ will be _grazing_, which will be a great advantage as compared with the _plunging_ fire that would be obtained from a position up the hill.