On the two subjects so much has already been written that it is impossible to find anything new to say about them. Only one point has not been brought out sufficiently--namely, that both security and reconnaissance, in so far as both depend on patrols, will only then work successfully when they are based on a thoroughly systematized method of procedure. The subject is of such importance that I have considered it necessary to devote a short chapter to it (Book I., Chap. VIII.). If reconnaissance--apart from the fact that the roads must be cleared for it in the first instance by the defeat of the enemy's Cavalry--lies exclusively in the hands of the patrols, nevertheless security depends on the arrangement and activity of the other branches, such as advance guards, rear guards, flanking detachments, and outposts, and the conduct of these depends, again, on thorough systematization. When on the move, safety lies in the distance that separates the main body from the advanced detachments, and it is scarcely necessary to point out that only systematic arrangements can guarantee the necessary time for the exploration of the ground and the enemy which is requisite for safety. Threatened flanks require special detachments, moving on the same level and at sufficient distance, and their co-operation will be insured by a careful regulation of the mutual rate of march. A uniform rate of advance in the whole mechanism is an essential condition of complete security. Hence every means must be exhausted down to the smallest detail. It will not be necessary to assign minor flanking detachments for the duration of a whole march. During such a period it is practically impossible to retain their relation to the main body without keeping them within sight, which in most cases is quite impracticable, for circumstances may suddenly check the main body, or necessitate a change of direction. To advise the flanking detachments of such occurrences will generally be impossible, or at any rate very difficult, if one has permanently detached them, and therefore has no certainty of finding them at any particular point. Hence it is advisable to work them always in sections--that is to say, when they have reached certain points to withdraw them to the main body, and send out reliefs for the next section. But in order that the security should never for one instant be relaxed, these fresh reliefs should always be sent out at some little distance before the point at which the former detachment is to be drawn in. Almost more important than security at night is security during prolonged periods of rest. In that case the arrangements must be made not only in accordance with tactical requirements, but the fact must be taken into account that horses, in order to remain permanently useful, require quite a different nature of rest than is needed by men.