s engaged in
withdrawing his lines with a view of taking a stronger position nearer
Richmond. General McClellan began a forward movement with the Army of
the Potomac on the 10th of March. The truth was that Confederate spies
in Washington had apprised Johnston of the intended advance of McClellan
from the lower Chesapeake, and his action was with a view of checkmating
the Union commander. Instead of carrying out this plan, McClellan
marched to Centreville and occupied the vacated intrenchments of the
enemy. The general hope was that Johnston would be forced to give
battle, but the roads in Virginia, at that season, were one sea of mud,
which made progress so slow that the Confederates had time in which to
withdraw at their leisure.

Crossing the Potomac into Virginia, with the main army, McClellan made
his first headquarters at Fairfax Court-House. About that time he
received news that he was relieved of the command of the other
departments, his authority being confined to the direction of the Army
of the Potomac. He was directed by the President to garrison Manassas
securely, see that Washington was protected, and, with the rest of his
force, assume a new base at Fort Monroe, or "anywhere between here and
there," and, above all things, to pursue the enemy "by _some_ route."

McClellan's four corps commanders were Sumner, McDowell, Heintzelman,
and Keyes, and they and he agreed upon a plan of campaign. The
difficulties of transporting nearly 100,000 men to Fort Monroe were so
great that two weeks were occupied in completing the transfer. In order
to prevent the Confederates from getting in his rear, McClellan directed
Banks to rebuild the railroad from Washington to Manassas and Strasburg,
thus keeping open communication with the Shenandoah Valley, where the
enemy were in force, a fact which caused the government much uneasiness
for the national capital. Indeed, it was a part of the effective plan of
Johnston to embarrass the campaign against Richmond.

Banks occupied Winchester about the middle of March and sent a force
under Shields to Strasburg. He found Stonewall Jackson there with such a
strong force that he fell back to Winchester, where, after the
withdrawal of the main body by Banks, he was attacked by Jackson, who
was repulsed.

In pursuance of the new plan of campaign, McClellan made Fort Monroe his
first base of operations, using the route through Yorktown and West
Point for the advance to Richmond. He ex