While lying at Frederick City, Lee conceived the bold and perilous project of again dividing his army in the face of his enemy, and that enemy McClellan.  Swinging back with a part of his army, he captured the stronghold of Harper’s Ferry, with its 11,000 defenders, while with the other he held McClellan at bay in front.  The undertaking was dangerous in the extreme, and with a leader less bold and Lieutenants less prompt and skillful, its final consummation would have been more than problematical.  But Lee was the one to propose his subalterns to act.  Harper’s Ferry, on the Virginia side of the Potomac, where that river is intersected by the Shenandoah, both cutting their way through the cliffs and crags of the Blue Ridge, was the seat of the United States Arsenal, and had immense stores of arms and ammunition, as well as army supplies of every description.  The Baltimore and Ohio Railroad and the canal cross the mountains here on the Maryland side, both hugging the precipitous side of the mountain and at the very edge of the water.  The approaches to the place were few, and they so defended that capture seemed impossible, unless the heights surrounding could be obtained, and this appeared impossible from a military point of view.  On the south side are the Loudon and Bolivar Heights.  On the other side the mountains divide into two distinct ranges and gradually bear away from each other until they reach a distance of three miles from crest to crest.  Between the two mountains is the beautiful and picturesque Pleasant Valley.  The eastern ridge, called South Mountain, commencing from the rugged cliff at Rivertoria, a little hamlet nestled down between the mountains and the Potomac, runs northwards, while the western ridge, called Elk Mountain, starts from the bluff called Maryland Heights, overlooking the town of Harper’s Ferry, and runs nearly parallel to the other.  Jackson passed on up the river with his division, Ewell’s, and A.P.  Hill’s, recrossed the Potomac into Virginia, captured Martinsburg, where a number of prisoners and great supplies were taken, and came up and took possession of Bolivar Heights, above Harper’s Ferry.  Walker’s Division marched back across the Potomac and took possession of Loudon Heights, a neck of high land between the Shenandoah and Potomac overlooking Harper’s Ferry from below, the Shenandoah being between his army and the latter place.  On the 11th McLaws moved out of Frederick City, strengthened by the brigades of Wilcox, Featherstone, and Pryor, making seven brigades that were to undertake the capture of the stronghold by the mountain passes and ridges on the north.  Kershaw, it will be seen, was given the most difficult position of passage and more formidable to attack than any of the other routes of approach.  Some time after Jackson and Walker had left on their long march, McLaws followed.  Longstreet and other portions of the army and wagon trains kept the straight road towards Hagerstown, while Kershaw and the rest