Many readers of Civil War history have been led to believe the battle of South Mountain (September 14, 1862) was but a trifling skirmish, a preliminary engagement of little strategic or tactical consequence overshadowed by Antietam s horrific carnage just three days later. In fact, the fight was a decisive Federal victory and important turning point in the campaign, as historian Brian Matthew Jordan argues convincingly in his fresh interpretation Unholy Sabbath: The Battle of South Mountain in History and Memory, September 14, 1862.Most writers brush past the mid-September battle in a few...