Before the last troops of the main column have quitted camp, the rear-guard commander should have arranged his force in a series of successive positions, calculated to enable the units to mutually support one another's retirement, as well as to assist, if necessary, the withdrawal of picquets. The guns should, for reasons already given, be kept well back, and this system of successive positions should be continued throughout the march. It is, of course, understood that the main column keeps contact with, and regulates its march by that of the rear-guard. It is sometimes advocated that the camp picquets should, before the column marches off, be relieved by the rear-guard, with the object of enabling the picquets to rejoin their units. This arrangement does not appear advantageous. The troops detailed for the relief of the picquets will probably have to move out in darkness, and over an unknown area, and though, if the enemy advances during the relief, he will be opposed in double strength, should his attack be delivered later, units who do not know the ground will be placed in positions they will not be able to defend to the best advantage. Besides, the men composing the rear-guard, whose functions are in any case sufficiently arduous, will be involved in additional and unnecessary fatigue. The withdrawal of picquets may be carried out on the following principles:-- When a picquet commander sees, or receives reports that the rear-guard is approaching, he should send the bulk of his picquet to a position, previously reconnoitred, on the lower slope of the hill, and in the direction of the line of march of the column, whence the retirement of the remainder can be covered by fire. Whilst on the hill, and especially as the time for withdrawal approaches, the men of a picquet should be careful not to show themselves, in order that the enemy may not, by counting heads, be able to divine that retirement has been begun. Similarly, the men left on the hill to the last, should, above everything, avoid exposure. When the picquet commander sees the rear-guard commander, who will usually be with the last troops, and whose presence will be shown by a flag, is opposite his post, he should give the signal for the evacuation of the hill top, on which the men should creep back, and as soon as they are below the sky line, run down the hill to a position beyond that of their covering party. The withdrawal should then be continued according to the accepted principles, until the whole picquet has reached the valley, when its leader should report to the rear-guard commander, receiving orders whether the picquet is to proceed to the main column, or to join the rear-guard. The rear guard commander should have previously called in the road sentry post marking the locality held by the picquet, and the map furnished by the advanced guard will have been of assistance in identifying its position. [Illustration]