The Gettysburg campaign began 150 years ago as Lee began breaking contact with the Federal army at Fredericksburg, Virginia. The Confederates filed off to the northwest, leaving A. P. Hill's Third Corps to cover the movement. Hooker heard of the movement, but Hill's troops were able to skirmish with him and stop him from pressing forward.
Lee's plan for his invasion of the north would be to move through the Shenandoah Valley. The mountain range to the east would screen him from Hooker's army and allow him to easily defend his line of march, using the mountain passes. First Ewell with the Second Corps would clear the Federal forces out of the valley. Then while Longstreet with the First Corps covered the east side of the Blue Ridge, Hill's Third Corps would follow Ewell down the Valley.