Lee's army, fifty thousand strong, had crossed the Potomac at Leesburg and had concentrated around Frederick, the scene of the Barbara Frietchie legend, only forty miles from Washington. When it became known that Lee, elated by his victory at Second Bull Run, had taken the daring step of advancing into Maryland, and now threatened the capital of the Republic, McClellan, commanding the Army of the Potomac, pushed his forces forward to encounter the invaders. Harper's Ferry, at the junction of the Potomac and the Shenandoah rivers, was a valuable defense against invasion through the Valley of Virginia, but once the Confederates had crossed it, a veritable trap. General Halleck ordered it held and General Lee sent "Stonewall" Jackson to take it, by attacking the fortress on the Virginia side. Jackson began his march on September 10th with secret instructions from his commander to encompass and capture the Federal garrison and the vast store of war material at this place, made famous a few years before by old John Brown. To conceal his purpose from the inhabitants he inquired along the route about the roads leading into Pennsylvania. It was from his march through Frederick that the Barbara Frietchie story took its rise. But there is every reason to believe that General Jackson never saw the good old lady, that the story is a myth, and that Mr. Whittier, who has given us the popular poem under the title of her name, was misinformed. However, Colonel H. K. Douglas, who was a member of Jackson's staff, relates, in "Battles and Leaders of the Civil War," an interesting incident where his commander on entering Middletown was greeted by two young girls waving a Union flag. The general bowed to the young women, raised his hat, and remarked to some of his officers, "We evidently have no friends in this town." Colonel Douglas concludes, "This is about the way he would have treated Barbara Frietchie." On the day after Jackson left Frederick he crossed the Potomac by means of a ford near Williamsport and on the 13th he reached Bolivar Heights. Harper's Ferry lies in a deep basin formed by Maryland Heights on the north bank of the Potomac, Loudon Heights on the south bank, and Bolivar Heights on the west. The Shenandoah River breaks through the pass between Loudon and Bolivar Heights and the village lies between the two at the apex formed by the junction of the two rivers.