In 1862, the Union reopened Illinois’s first state penitentiary, in Alton, as a prison for Confederate soldiers. Over the next three years about 11,700 people passed through it, including Confederate soldiers, Union deserters, accused guerrillas and civilians, several of them women. No fewer than 1,500 died, mostly of disease. A monument in town lists 1,534 Confederate names. The prison itself is gone. What remains is the outer corner of one wall.

The building was never lucky. It opened in 1833 with 24 cells, grew to 256, and was abandoned in the 1850s after complaints about its damp, unhealthy site. When the war filled it with prisoners, the problems came back at scale: chronic overcrowding, latrines too close to the drinking water, cells packed so tightly that men reportedly couldn’t lie down or unfold their knees. Pneumonia and dysentery did most of the killing. Smallpox arrived too.

The smallpox response was to move the sick onto the river. Two hastily built hospitals went up on islands in the Mississippi, Sunflower Island, later called Smallpox Island, and Tow Island. An estimated 240 Confederate soldiers, and an unknown number of Union guards, died and were buried on Tow Island. Hundreds more went into a burial ground north of town, the same plot the state used for penitentiary prisoners before the war. The islands are mostly underwater now, reshaped by decades of river and flood.

Alton is billed as one of the most haunted small towns in America, and the Riverfront Times has called it Mid-America’s most haunted town. The prison wall is a stop on the Alton Hauntings walking ghost tour, and the Confederate cemetery gets similar billing. It is easy to see why the tours stop there: the wall is the only part of the prison left standing, and the dead are mostly under a river or in a cemetery north of town.

The ghost tours are the folklore. The numbers are the record. About 11,700 people came through the gate, at least 1,500 didn’t leave, and the monument lists 1,534 of them by name. The names are the only part that isn’t a story.