Photos from Antietam National Battlefield at Sharpsburg, Maryland. According to the National Park Service site for Antietam, the 12-hour Civil War battle that occurred there September 17, 1862, is the bloodiest one-day battle in American history. In that day, the two sides combined suffered nearly 23,000 casualties -- killed, wounded, and missing; 3,654 were killed in battle (1,546 Confederate and 2,108 Union). Except for the monuments and signs commemorating the battle, the peaceful setting that is now Antietam National Battlefield gives no hint of its violent past. In addition to the National Park Service site for Antietam National Battlefield, a very useful source of information is the recent (but undated) monograph, The Battle of Antietam: September 17, 1762, written by John D. Hoptak, designed and illustrated by Keith D. Snyder, and published by Western Maryland Interpretative Association (WMIA); for example, a breakdown of the 23,000 total casualties by type and side appears on page 70. WMIA is identified on the Antietam Partner website as "the nonprofit cooperating association for Antietam National Battlefield".