=70.= =The Investment.=--The investing force is brought together, organized, and moved rapidly upon the place. When it is available a large force of mounted troops may be used advantageously in the investment, and be subsequently relieved by infantry and artillery. When the investment is made, it adds greatly to the advantage of the attack to completely surround and isolate the work, and to push the investing line as near it as possible. When the investing force is more or less dispersed, and is to be concentrated for the siege, the temptation frequently exists to march them by converging lines upon the place as a point of concentration. While this may be advisable in some cases (as where the garrison is very weak or under an inefficient commander), it will usually expose the subdivisions of the investing force to be beaten in detail (Art of War, par. 392). So also in surrounding the place; a premature subdivision of the force into small fractions not protected by field-works, or not within supporting distance each other, will afford to an active defence an opportunity, by well-conducted sorties, to inflict most severe losses upon the attack and very greatly delay the investment. Keeping these dangers in view, the investing force will move rapidly upon the work, seize, strengthen, and occupy strong points as near the work as possible, and extend the lines to right and left as rapidly as good judgment allows, until the place is surrounded. Meanwhile detachments of greater or less size will scour the ground around the place, seizing and carrying off or destroying, so far as possible, all cattle, grain, lumber, etc., and everything else which would be of use to the attack or defence. Under cover of these detachments and escorts specially detailed for the purpose, reconnoissances will be made to cover so much of the ground as can be reached, especial efforts being made to examine the ground near the works. These reconnoissances will necessarily be hurried and incomplete but, must be as accurate as they can be made under the circumstances. They should be directed principally to determining the heights and directions of the principal points of the works, and their positions with reference to prominent points that may be used as landmarks, in verifying and correcting maps and information previously obtained, to discovering the existing armament of the place and the steps already taken for its defence, and to collecting all possible information bearing upon the selection of the front of attack. Systematic reconnoissances and surveys carried on throughout the siege must be relied upon for checking and completing the work thus begun.