On September 16, 1862, Major General George B. McClellan confronted General Robert E. Lee's Army of Northern Virginia at Sharpsburg, Maryland. At dawn September 17, Brigadier-General Joseph Hooker's corps mounted a powerful assault on Lee's left. Attacks and counterattacks swept across Miller's cornfield and fighting swirled around the Dunker Church. Union assaults against the Sunken Road eventually pierced the Confederate center, but the Federal advantage was not followed up. Late in the day, Brigadier-General Ambrose E. Burnside's corps finally got into action, crossing the stone bridge over Antietam Creek. At a crucial moment, A.P. Hill's division arrived from Harpers Ferry and counterattacked, driving back the Federal forces. Although outnumbered two-to-one, Lee committed his entire force, while McClellan sent in less than three-quarters of his army, enabling Lee to fight the Federals to a standstill. In spite of crippling casualties, Lee continued to skirmish with McClellan throughout the 18. McClellan did not renew the assaults, allowing Lee to withdraw the battered Army of Northern Virginia across the Potomac into the Shenandoah Valley.
