The roads which lead from the position of an army to those points in its rear where its depôts of supply and means of recruiting and refitting its forces are principally united, and which it also in all ordinary cases chooses for its retreat, have a double signification; in the first place, they are its lines of communication for the constant nourishment of the combatant force, and next they are roads of retreat.
We have said in the preceding chapter, that, although according to the present system of subsistence, an army is chiefly fed from the district in which it is operating, it must still be looked upon as forming a whole with its base. The lines of communication belong to this whole; they form the connection between the army and its base, and are to be considered as so many great vital arteries. Supplies of every kind, convoys of munitions, detachments moving backwards and forwards, posts, orderlies, hospitals, depôts, reserves of stores, agents of administration, all these objects are constantly making use of these roads, and the total value of these services is of the utmost importance to the army.
These great channels of life must therefore neither be permanently severed, nor must they be of too great length, or beset with difficulties, because there is always a loss of strength on a long road, which tends to weaken the condition of an army.
By their second purpose, that is as lines of retreat, they constitute in a real sense the strategic rear of the army.
For both purposes the value of these roads depends on their length , their number , their situation , that is their general direction, and their direction