This is one of the most famous photographs Alexander Gardner took following the Battle of Antietam. It is believed he began taking his photos on the morning of September 19, 1862, two days after the fighting. Many dead Confederate soldiers could still be seen where they had fallen. Union burial details had already spent a day working to bury federal troops.
The dead men in this photograph most likely belonged to an artillery crew, as they are lying dead beside an artillery limber. And it is known that Confederate guns in this position, in the vicinity of the Dunker Church, the white structure in the background, played a role in the battle.
The Dunkers, incidentally, were a pacifist German sect. They believed in simple living, and their church was a very basic meeting house with no steeple.