The Battle of South Mountain, known in several early Southern accounts as the Battle of Boonsboro Gap, was fought on September 14, 1862, as part of the Maryland campaign of the American Civil War. Three pitched battles were fought for possession of three South Mountain passes: Crampton's, Turner's, and Fox's Gaps.

The Maryland campaign occurred September 4–20, 1862, during the American Civil War. The campaign was Confederate General Robert E. Lee's first invasion of the North. It was repulsed by the Army of the Potomac under Maj. Gen. George B. McClellan, who moved to intercept Lee and his Army of Northern Virginia and eventually attacked it near Sharpsburg, Maryland. The resulting Battle of Antietam was the bloodiest day of battle in American history.