History.com: How Photos From the Battle of Antietam Revealed the American Civil War's Horrors

In October 1862, a shocking and unique photo exhibition opened at Mathew B. Brady's Broadway gallery in New York City. A small placard at the door advertised "The Dead of Antietam," and, as The New York Times reported on October 20, "crowds of people are constantly going up the stairs," drawn by the "terrible fascination" of seeing gruesome photographs of bloated, dead bodies of soldiers as they fell in combat on the battlefield of Antietam during the Civil War.