How much more was this true when {p.307} a great further advance of 250 miles was intended.
In short, before moving forward, it was necessary to insure that the connection behind was established, and the provision for transport ahead adequately developed.

This involved not only an immense accumulation of animals, to allow for a waste always extreme, but also large reinforcements of troops; for every step forward in an enemy's country requires a detachment left behind to secure it.
"At each remove the lengthening chain" demands its group of guards, and these wisely disposed for quick mutual assistance; for with any enemy, and especially with one so mobile, it is impossible to be everywhere in sufficient force, superior to an unexpected attack.
Communications are ever on the defensive, the most embarrassing of military attitudes.

To the scattered units of such a system, all that can be provided is power to hold out until succoured.

Moreover, there must be not merely a steady stream of supply from some far distant source, but the establishment of intermediate reservoirs--secondary depots--well stored with the manifold requirements of {p.308} an army in campaign; advanced bases, capable by themselves of supporting for an appreciable time the existence and activity of forces dependent upon them alone.

The importance of these to the army make them ever an object of attack to the enemy.