than 12,000 Union prisoners, then led most of his men to join Lee at Sharpsburg, leaving Maj. Gen. A.P. Hill's division to complete the occupation of the town. South Mountain Pitched battles were fought on September 14 for possession of the South Mountain passes: Crampton's, Turner's, and Fox's Gaps. Maj. Gen. D.H. Hill defended Turner's and Fox's Gaps against Burnside. To the south, Maj. Gen. Lafayette McLaws defended Crampton's Gap against Franklin, who was able to break through at Crampton's Gap, but the Confederates were able to hold Turner's and Fox's, if only precariously. (For the counter argument that the Union held Fox's Gap, see Older, Curtis L., Hood's Defeat Near Fox's Gap September 14, 1862.) Lee realized the futility of his position against the numerically superior Union forces, and he ordered his troops to Sharpsburg. McClellan was then theoretically in a position to destroy Lee's army before it could concentrate. McClellan's limited activity on September 15 after his victory at South Mountain, however, condemned the garrison at Harpers Ferry to capture and gave Lee time to unite his scattered divisions at Sharpsburg. Antietam (Sharpsburg) On September 16, McClellan confronted Lee near Sharpsburg. Lee was defending a line to the west of Antietam Creek. At dawn on September 17, Maj. Gen. Joseph Hooker's I Corps mounted a powerful assault on Lee's left flank that began the bloody battle. Attacks and counterattacks swept across the Miller Cornfield and the woods near the Dunker Church as Maj. Gen. Joseph K. Mansfield's XII Corps joined to reinforce Hooker. Union assaults against the Sunken Road ("Bloody Lane") by Maj. Gen. Edwin V. Sumner's II Corps eventually pierced the Confederate center, but the Federal advantage was not pressed. In the afternoon, Burnside's IX Corps crossed a stone bridge over Antietam Creek and rolled up the Confederate right. At a crucial moment, A.P. Hill's division arrived from Harpers Ferry and counterattacked, driving back Burnside's men and saving Lee's army from destruction. Although outnumbered two to one, Lee committed his entire force, while McClellan sent in only four of his six available corps. This enabled Lee to shift brigades across the battlefield and counter each individual Union assault. During the night, both armies consolidated their lines. In spite of crippling casualties—Union 12,401, or 25%; Confederate 10,316, or 31%—Lee continued to skirmish with McClellan throughout September 18, while transporting his wounded men south of the Potomac. McClellan did