Volunteers are lighting more than 23,000 candles at the Antietam National Battlefield near Sharpsburg to honor those were killed, wounded or declared missing in the Civil War's bloodiest one-day battle.
Saturday's annual illumination is a drive-through event. Organizers expect as many as 20,000 visitors to take the five-mile tour and reflect on the battle.
The clash near Sharpsburg on Sept. 17, 1862, lasted from dawn to dusk with no clear winner. President Abraham Lincoln viewed the next day's Confederate retreat as divine approval for abolishing slavery.
He issued the preliminary Emancipation Proclamation five days later.