<human>:  When did the Battle of Antietam take place?
<bot>: The Battle of Antietam took place on September 17, 1862. The Battle of Antietam was a major battle of the American Civil War, fought in the Maryland Campaign of 1862. The Union Army of the Potomac, under the command of Maj. Gen. George B. McClellan, fought against the Confederate Army of Northern Virginia, under the command of Lt. Gen. Robert E. Lee.