Antietam National Cemetery

Blue orbs of light drift between the headstones at dusk, moving in rhythm with a phantom drum that beats military cadence and then fades. The cemetery holds 4,776 Union soldiers from the bloodiest day in American history, 1,836 of them unidentified, on 11 acres purchased for $1,161.75 in 1865.

Blue lights float over the headstones. Visitors to Antietam National Cemetery at dusk have described small orbs of blue light drifting between the graves, moving in rhythm, as if keeping pace with a phantom drum that beats out a cadence and then fades into the distance. Nobody has been able to photograph the lights clearly. Nobody has been able to explain them, either.

The cemetery sits on 11 and a quarter acres of land purchased on March 23, 1865, for $1,161.75. The math comes out to about $103 per acre, a price tag for ground that holds 4,776 Union soldiers killed in the bloodiest single day in American history. Of those 4,776, a total of 1,836 are unknown, roughly 38 percent. Two men named Aaron Good and Joseph Gill spent months after the war identifying remains by whatever they could find on the bodies: letters, receipts, diaries, photographs, marks on belts or cartridge boxes. They interviewed survivors whenever possible. For the remaining 1,836, there was simply nothing to go on. No name, no regiment, no home state. Just bones in Maryland soil.

The work force that built the cemetery was composed primarily of honorably discharged soldiers. Construction took about two years. The cemetery was completed by September 1867, and President Andrew Johnson attended the dedication on September 17, the fifth anniversary of the battle. Johnson said: "When we look on yon battlefield, I think of the brave men who fell in the fierce struggle of battle, and who sleep silent in their graves."

"Silent" may not be the right word anymore. Visitors walking through the burial rows have heard soft sobbing, the muffled sound of mourning that seems to come from the ground rather than from any person nearby. One visitor reported watching a wisp of mist rise from the earth and disappear into a headstone while he was taking photographs. He had no explanation for what he saw. The phantom drum is the most common report. People describe it as military cadence, a snare drum keeping time for a march, growing louder as if approaching and then fading as if the drummer is passing through on his way somewhere else. The sound carries across the hillside and then dies out over the fields where the battle was fought.

The cemetery layout is organized by state. Connecticut, Delaware, Indiana, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Vermont, West Virginia, Wisconsin, and a section for regulars and unknowns. Each state section has its own arc of headstones radiating from the center monument. Walking through, the geographic spread hits differently than a casualty number. These men came from everywhere.

The Private Soldier Monument at the center was dedicated on September 17, 1880, eighteen years after the battle. The statue stands 44 feet and 7 inches tall, with the soldier figure alone measuring 21 and a half feet. The whole structure weighs 250 tons, assembled from 27 pieces of granite. James G. Batterson of Hartford, Connecticut designed it. James Pollette of Westerly, Rhode Island sculpted it. The cost exceeded $32,000, which in 1880 was a serious number. The inscription reads: "Not for themselves, but for their country."

After the Civil War dead, the cemetery accepted burials from the Spanish-American War, World War I, World War II, and Korea. Burials stopped in 1953. Over 200 non-Civil War veterans are interred here, making the cemetery a compressed timeline of American conflict, all on a hillside overlooking the fields where 22,726 men fell between dawn and dusk on a single September day.

The blue lights have never been satisfactorily explained. Some theories point to swamp gas or bioluminescence from decomposition. Others suggest tricks of light on old stone. The drum has no theory at all. The cemetery closes at dusk, which means most of the reported phenomena happen right around the time visitors are walking back to their cars, catching something at the edge of their vision that they will spend the drive home trying to rationalize. The ground here absorbed 4,776 men in two years. Whatever it held onto, it has been letting pieces of it go, slowly, for 160 years.