“The plan of campaign I adopted during this advance,” he says, “was to move the army well in hand, parallel to the Blue Ridge, taking Warrenton as the point of direction for the main army, seizing each pass on the Blue Ridge by detachments as we approached it, and guarding them after we had passed, as long as they would enable the enemy to trouble our communications with the Potomac....  We depended upon Harper’s Ferry and Berlin for supplies until the Manassas Gap Railway was reached.  When that occurred, the passes in our rear were to be abandoned, and the army massed ready for action or movement in any direction.  It was my intention, if, upon reaching Ashby’s or any other pass, the enemy were in force between it and the Potomac, in the Valley of the Shenandoah, to move into the Valley and endeavor to gain their rear.”

From this statement of General McClellan it will be seen that his plan was judicious, and displayed a thorough knowledge of the country in which he was about to operate.  The conformation of the region is peculiar.  The Valley of the Shenandoah, in which Lee’s army lay waiting, is separated from “Piedmont Virginia,” through which General McClellan was about to advance, by the wooded ramparts of the Blue Ridge Mountains, passable only at certain points.  These gaps, as they are called in Virginia, are the natural doorways to the Valley; and as long as General McClellan held them, as he proposed to do, by strong detachments, he would be able both to protect his own communications with the Potomac, and, if he thought fit to do so, enter the Valley and assail the Confederate rear.  That he ever seriously contemplated the latter design is, however, extremely doubtful.  It is not credible that he would have undertaken to “cut off” Lee’s whole army; and, if he designed a movement of that description against any portion of the Southern army which might be detached, the opportunity was certainly presented to him by Lee, when Jackson was left, as will be seen, at Millwood.

No sooner had General McClellan commenced crossing the Potomac, east of the mountain, than General Lee broke up his camp along the Opequan, and moved to check this new and formidable advance into the heart of Virginia.  It was not known, however, whether the whole of the Federal forces had crossed east of the Blue Ridge; and, to guard against a possible movement on his rear from the direction of Harper’s Ferry, as well as on his flank through the gaps of the mountain, Lee sent Jackson’s corps to take position on the road from Charlestown to Berryville, where he could oppose an advance of the enemy from either direction.  The rest of the army then moved guardedly, but rapidly, across the mountain into Culpepper.