General McClellan was accordingly directed, after General Pope's defeat, to take command of every thing, and see to the safety of Washington; and, finding himself at length at the head of an army of about one hundred thousand men, he proceeded, after the manner of a good soldier, to protect the Federal capital by advancing into upper Maryland in pursuit of Lee.
III.
MOVEMENTS OF THE TWO ARMIES.
General Lee was already moving to the accomplishment of his designs, the capture of Harper's Ferry, and an advance into the Cumberland Valley.
His plan to attain the first-mentioned object was simple, and promised to be successful.

Jackson was to march around by way of "Williamsport and Martinsburg," and thus approach from the south.

A force was meanwhile to seize upon and occupy the Maryland Heights, a lofty spot of the mountain across the Potomac, north of the Ferry.

In like manner, another body of troops was to cross the Potomac, east of the Blue Ridge, and occupy the Loudon Heights, looking down upon Harper's Ferry from the east.

By this arrangement the retreat of the enemy would be completely cut off in every direction.