22. _Positions._—Every military position ought to possess decided advantages of situation, and ought to be commanded in no part of its front, flank, or rear. All commanding grounds ought to be without the range of cannon. There are four principal objects to be attended to in the choice of a position: 1st. The advantages of the ground; 2d. The supplies for the army; 3d. The objects to be attained; and, 4th. The communications with the rear. The front of a position should be intersected by rivers, ravines, or broken ground, or any other obstacles which can prevent the enemy advancing in order of battle, and oblige him to pass through defilés; but a position becomes useless when the front is so covered by obstacles that the army cannot advance or move out of its camp when necessary; but no obstacles can be too great on the flanks. All obstacles which cover a position, or passes which lead to it, must be within the range of the artillery, or the enemy will pass them unmolested. In a flat country, where the ground does not afford commanding situations, a position is only more or less eligible, as being covered or protected by obstacles; these are very thick woods, in which there are very few roads; large rivulets which cannot be forded or passed without bridges; narrow roads; deep and broken ravines; ground much intersected with hedges, ditches, &c. but it is essential that all these obstacles should be under the fire of the artillery. It is always dangerous to occupy a position, which has its rear so covered by swamps, crossed by rivers or ravines, &c. as to render the retreat of the army difficult. The number of passes by which an army can retire must be examined and secured, and should never be less than 5 or 6. The rivers, brooks, &c. in front of a position, should never be depended upon for a supply of water, as the enemy may cut them off. The ground for a camp should not be too much intersected by hedges, ditches, or ravines, which occasion great intervals in the line, and obstruct the communications through the camp.