The Battle of South Mountain was fought on September 14, 1862 in Maryland’s South Mountain between Confederate and Union forces. The Battle of South Mountain was a very important battle. It was the first major battle fought north of the Potomac River. It was the first invasion of the Northern United States by a Confederate Army. It was also here and not at Antietam where the Confederates under General Robert E. Lee were defeated and turned back. The day-long pitched battle was fought for control of the three passes through the mountain: Crampton's, Turner's, and Fox's Gaps.