After learning that Confederate Gen. Jubal A. Early had taken half of his army north to Martinsburg, West Virginia, Union Gen. Philip H. Sheridan planned to move quickly on September 19, 1864, destroy the remaining Confederate force in Winchester, and cut off Early. The day began well as Sheridan's cavalry secured Spout Spring, where the Berryville Pike crosses Opequon Creek about 2.5 miles east, and pushed the Confederates back through the narrow Berryville Canyon. Once out of the 2-mile-long ravine, the Federals took the open ground on both sides of the pike, including the area where Millbrook High School now stands. But Union Gen. Horatio Wright, commanding the 6th Corps, let his supply wagons follow his troops into the canyon before Gen. William Emory's 19th Corps, despite Sheridan's instructions. Capt. John DeForest called it a "stupendous oversight" because the infantry column was split in two by miles of wagons. In the narrow ravine the wagon train became badly tangled, creating chaos among wagons, wounded, horses, and men, and Wright's attempt to send the wagons back only made matters worse. The delay kept Emory's troops from joining the field until nearly 11:00 a.m. and cost Sheridan almost three hours, giving Jubal Early time to assemble his widely scattered army on the battlefield and ending Sheridan's hope for a quick, easy victory. African-American Thomas Laws risked his life to smuggle vital information about Confederate troop movements to Sheridan, prompting his decision to attack on September 19.