It has become my custom on 9/11 to think back to a different day during a different September when America suffered an even more catastrophic loss of life. As I first explained in 2012, the events of Sept. 11, 2001 and Sept. 17, 1862, have become inextricably linked in my mind. In recognition of both events—and as a continuing cautionary tale against forgetting either of them—I offer a repost of a reflection I put up during ECW’s first year, Remembering 9/11 and the Lesson of Antietam.