For his movement two plans presented themselves: One to cross the Rapidan below Lee, moving by his right flank; the other above, moving by his left.
Each presented advantages over the other, with corresponding objections.
By crossing above, Lee would be cut off from all chance of ignoring Richmond or going north on a raid.

But if we took this route, all we did would have to be done whilst the rations we started with held out; besides, it separated us from Butler, so that he could not be directed how to cooperate.

If we took the other route, Brandy Station could be used as a base of supplies until another was secured on the York or James rivers.

Of these, however, it was decided to take the lower route.
The following letter of instruction was addressed to Major-General B.F.
Butler: "FORT MONROE, VIRGINIA, April 2, 1864.
"GENERAL:-In the spring campaign, which it is desirable shall commence at as early a day as practicable, it is proposed to have cooperative action of all the armies in the field, as far as this object can be accomplished.
"It will not be possible to unite our armies into two or three large ones to act as so many units, owing to the absolute necessity of holding on to the territory already taken from the enemy.

But, generally speaking, concentration can be practically effected by armies moving to the interior of the enemy's country from the territory they have to guard.