In the second week of September 1862, Lee broke his Army of Northern Virginia into four different sections. He and James Longstreet led the main body, which continued to forage, while three other sections, one of them led by Stonewall Jackson, moved against Harpers Ferry.

This move was something of a comedown for Lee; he had already accepted the truth that Maryland would not rise for the Southern cause. So long as his main force was not threatened, it made perfect sense to attack Harpers Ferry, which had many muskets, rifles, and cannon, all of which could be employed for the Confederate cause. Lee took a major risk dividing his army into so many sections, however; the very fact of his doing so indicates the level of contempt he had for McClellan. All might have been well had two Union soldiers not found a message from Lee.