While Imboden's wagons moved northwest, Lee designated a shorter route for his three corps: southwest through Fairfield and over Monterey Pass to Hagerstown. After dark on July 4, Lt. Gen. A.P. Hill's Third Corps headed out onto the Fairfield Road, followed by Lt. Gen. James Longstreet's First Corps and Lt. Gen. Richard S. Ewell's Second Corps. Lee accompanied Hill at the head of the column. Departing in the dark, Lee had the advantage of getting several hours head start and the route from the west side of the battlefield to Williamsport was about half as long as the ones available to the Army of the Potomac.