After sunset on September 14, 1862, Confederate cannons across the road on School House Ridge vanished in the darkness as shell-shocked Union soldiers on Bolivar Heights wondered whether they could survive another day of artillery bombardment. The Union troops could not rest, because General "Stonewall" Jackson's Confederate army might charge over School House Ridge at any moment. To guard against such an attack, the Union command established a human alarm system on this field in the form of a skirmish line, the first line of defense, so that if the Confederates advanced, the gunfire from the Union soldiers on the skirmish line would reveal the location of the attack. "Stonewall" Jackson was counting on it.