This rule does not require that _all the army should occupy the same position_.

Far from it.

Concentration requires the main body to be in immediate and supporting reach: small detachments, for temporary and important objects, like those mentioned, are perfectly legitimate, and in accordance with correct principles.

Napoleon's position in Spain will serve as an illustration.

A hand, placed on the map of that country, will represent the position of the invading forces.
When opened, the fingers will represent the several detachments, thrown out on important strategic lines, and which could readily be drawn in, as in closing the hand, upon the principal and central mass, preparatory to striking some important blow.
"If, as we have seen, it be the first great rule for an army acting on the offensive principle, to keep its forces _concentrated_, it is, no doubt, the second, _to keep them fully employed._ Is it your intention to seize a particular province of your enemy?
to penetrate to his capital?
or to cut him off from his supplies?
Whatever measure be necessary to open your route to these objects must be _promptly_ taken; and if you mean to subsist yourself at his expense, your movements must be more rapid than his.