Roughly speaking, it may be said that about 100 men per mile suffice for all protective purposes, and it is assumed that the responsibility of a staging post commandant extends half way to the posts on either side of his own. The garrison of a staging post must be of sufficient strength, and of suitable composition, to secure the convoys halting there for the night, to furnish them with police escorts for the next day's march, and, if road picquets are found from the post, to supply these also. Road picquets can either be sent out each day from staging posts, can be permanently located in a succession of blockhouses, or can be semi-permanent, that is to say can be supplied from a series of minor posts connecting staging centres. In each of the above cases the same number of men will be required. The first method, by concentrating the troops each evening, makes for their general security, but, since picquets must daily, and at fixed hours, move to and from their places, a good deal of fatigue will be imposed on the men, and there will, in addition, be some risk of minor disasters to individual picquets, which may be ambuscaded. Moreover, since the convoys cannot march until the picquets are in position, and as picquets cannot be risked outside the post before sunrise and after sunset, the hours available for the movements of the convoys will be a good deal curtailed. Under the second alternative, a weak cordon is formed, portions of which cannot, owing to the topography, easily render one another support in case any picquet is attacked in force. On the other hand, no time will be wasted in posting and withdrawing picquets. The third system is a compromise between the two already mentioned, and seems, on the whole, to be the most advantageous. If three or four relatively large posts are placed, in dangerous localities, such as valley junctions, between staging centres, there will be little or no risk of their capture by the enemy. Since the picquets necessary to watch, by day, the area between the posts, will have but short distances to traverse to reach their positions, the time available for movement of convoys will not be curtailed; and as the ground intervening between two posts will, in some degree, be overlooked from them, there will be less chance, than under the first method, of picquets falling into ambuscades. The efficiency of the protection of a line of communication depends, however, on the active, not on the passive measures for its security.