Early got off to a good start. He drove down the Valley without opposition, bypassed Harpers Ferry, crossed the Potomac River, and advanced into Maryland. Grant dispatched a corps under Maj. Gen. Horatio G. Wright and other troops under Crook to reinforce Washington and pursue Early. Early defeated a smaller force under Maj. Gen. Lew Wallace in the Battle of Monocacy on July 9, but this battle delayed his progress enough to allow time for the reinforcement of the defenses of Washington. Early attempted some tentative attacks against Fort Stevens (July 11–12) on the northern outskirts of Washington, but then withdrew to Virginia. A number of small battles ensued as the Union pursued, including the defeat of Crook at the Second Battle of Kernstown on July 24.