After his success at Second Manassas, Gen. Robert E. Lee led the Army of Northern Virginia north across the Potomac River on an invasion of Maryland in early September, 1862. Lee divided his army, sending Lieut. Gen. James Longstreet into western Maryland while Lieut. Gen. “Stonewall” Jackson attempted to capture the Federal garrison at Harper's Ferry. The bold plan was jeopardized on September 13 when a mislaid copy of Lee's orders revealing the Confederates' plans was given to Union commander Maj. Gen. George B. McClellan. The next day, emboldened by this intelligence, McClellan moved his army toward the three passes on South Mountain to destroy the Confederate defenders there and divide Lee's army. Maj. Gen. Joseph Hooker at Turner's Gap, Maj. Gen. Jesse Reno at Fox's Gap, and Maj. Gen. William B. Franklin at Crampton's Gap all gained some success against Maj. Gen. D. H. Hill and his reinforcements. Finally defeated in battle by McClellan, Lee withdrew. Though the Federals ultimately gained control of all three passes, stubborn resistance on the part of the Southerners bought Lee precious time to begin the process of reuniting his army, and set the stage for the Battle of Antietam three days later.