The Battle of Manassas Gap, also known as the Battle of Wapping Heights, took place on July 23, 1863, in Warren County, Virginia, at the conclusion of General Robert E. Lee's retreat back to Virginia in the final days of the Gettysburg Campaign of the American Civil War. Union forces attempted to force passage across the Blue Ridge Mountains and attack the Confederate rear as it formed a defensive position in the upper Shenandoah Valley. Despite successfully forcing the passage at Manassas Gap, the Union force was unable to do so before Lee retreated further up the valley to safety, resulting in an inconclusive battle.