The temporary positions taken on this line become strategic positions, and the line in his rear, a line of defence.

When he arrives in the vicinity of his first object, and the enemy begins to oppose his enterprises, he must force this enemy to retreat, either by an attack or by manoeuvres.

For this purpose he temporarily adopts certain lines of manoeuvre, which may deviate from his general line of operations.

The ulterior events of the campaign may possibly cause him to make these new, or accidental lines, his lines of operations.

The approach of hostile forces may cause him to detach secondary corps on secondary lines; or to divide his army, and pursue double or multiple lines.