this kind, usually divides itself into four or five principal posts.
For important points of approach, beyond a certain distance, and yet in some measure threatened, special central points are established which, in a certain measure, form small theatres of war within the principal one. In this manner the Austrians, during the Seven Years’ War, generally placed the main body of their army, in four or five posts in the mountains of Lower Silesia; whilst a small almost independent corps organised for itself a similar system of defence in Upper Silesia.
Now, the further such a defensive system diverges from direct covering, the more it must call to its assistance—mobility (active defence), and even offensive means. Certain corps are considered reserves; besides which, one post hastens to send to the help of another all the troops it can spare. This assistance may be rendered either by hastening up directly from the rear to reinforce and re-establish the passive defence, or by attacking the enemy in flank, or even by menacing his line of retreat. If the assailant threatens the flank of a post not with direct attack, but only by a position through which he can act upon the communications of this post, then either the corps which has been advanced for this purpose must be attacked in earnest, or the way of reprisal must be resorted to by acting in turn on the enemy’s communications.