When the train transporting the first Union prisoners of war to Andersonville finally exhaled after a week-long trip from Richmond, Virginia, its human cargo breathed a sigh of relief as well. The Union prisoners who arrived at Camp Sumter on February 24, 1864, had just survived a harsh winter, meager rations and severe overcrowding in Virginia. They knew little about their new home in remote southwest Georgia except this—no place could be more horrible than Richmond. They were wrong.

When the prisoner-exchange system between the Union and the Confederacy collapsed in the summer of 1863 over its applicability to black soldiers and their white officers, prison populations in both the North and South soared. As the number of detainees swelled, so did the awful conditions they endured. By late 1863, the situation had become particularly dire in Richmond, where one out of every five people in the city were Union prisoners. The city buckled under the weight of its 15,000 captives, who lacked adequate shelter, food and water. Ninety percent of the survivors inside the Belle Isle prison weighed less than 100 pounds. A humanitarian crisis gripped Richmond, and the security threat of having so many enemy forces housed in the Confederate capital alarmed Southern military brass.

Andersonville was to be the solution to Richmond’s problem. In early 1864, the Confederacy began construction of Camp Sumter on a patch of land with salubrious air and the pristine waters of Sweet Water Branch. The Confederate military impressed hundreds of slaves to clear-cut the tall Georgia pines and construct the 16.5-acre camp, which meant that Union soldiers weren’t the first people brought to Andersonville against their own will.

When more than 100 Union soldiers escaped from a Richmond prison on February 9, 1864, the Confederacy decided that it could wait no longer. The transportation of Union prisoners began, although Camp Sumter was far from complete when the first 400 captives arrived. A lack of wooden barracks forced prisoners to live in makeshift tents stitched together by blankets and scraps of wood held up by sticks as brittle as they were.

Trains hauling hundreds of prisoners arrived each day, and by May 1864 the Andersonville prison reached its capacity of 10,000. The trains, however, kept on coming. Although Camp Sumter was expanded by 10 acres, it did little to ease the cramped conditions for the 26,000 prisoners stuffed inside what they called a “bull pen.” The inmates were confined like livestock in a space less than six football fields long and three football fields wide surrounded by a 15-foot-tall wooden stockade. A low rail fence 19 feet inside the camp’s enormous walls was delineated as the “dead line,” a common form of crowd control in Civil War military prisons. Any prisoner who crossed the barrier risked being shot on sight by the armed soldiers who roosted in the guard towers atop the stockade.

Conditions reached their nadir in August 1864 when the prison population surpassed 33,000, three times its original capacity. If it had been a municipality, Camp Sumter would have been the fifth-biggest city in the Confederacy, and indeed urban-sounding thoroughfares with names like Market Street and Broad Street knifed through the collection of makeshift tents. The Confederacy lacked sufficient supplies to feed this mini-city. Daily rations were meager—a teaspoon of salt, three tablespoons of beans and a half-pint of unsifted cornmeal. And by that point, there was nothing sweet about Sweet Water Branch, which doubled as a sewer and drinking water source. Sickness raced through the camp as quickly as the filthy creek itself.

Three thousand prisoners at Andersonville died in August 1864 alone—an average of one death every 11 minutes. Each morning at the camp’s gate, emaciated, half-clothed bodies were laid out in the blistering heat for pickup by the horse carts for burial in the network of shallow trenches.

Once Union General William Tecumseh Sherman captured Atlanta in September 1864, the Confederacy evacuated the majority of Andersonville’s prisoners to other camps to prevent their mass liberation. By November 1864, the prison population had plummeted to 4,000, and by Christmas the stockade was virtually empty, with most of the remaining prisoners in the hospital. The prisoner camp closed at war’s end in the spring of 1865.

Even by the terrible standards of both Union and Confederate prisoner of war camps, where more than 50,000 from both sides of the Civil War died, the mortality rate at Andersonville was astronomical. Camp Sumter held 10 percent of all Civil War prisoners yet accounted for 23 percent of the war’s prisoner deaths. Even during the 10 of its 14 months of Andersonville’s operation when the prisoner population was under its intended capacity, the death rate was staggering. During November 1864, nearly half of the Union prisoners perished.

Death and tragedy connected to Andersonville did not end with the war, however. Numerous Andersonville survivors finally returning home were among the estimated 1,800 victims aboard the steamship Sultana that exploded on April 27, 1865, as it paddled up the Mississippi River. Swiss immigrant Henry Wirz, who commanded Camp Sumter, was convicted of murder and conspiracy to injure the health and lives of Union soldiers by a military tribunal. Although he insisted that he was simply following orders, Wirz was executed by hanging in the shadow of the Capitol dome inside a Washington, D.C., prison yard on November 10, 1865.

Back in Andersonville, the work continued to replace the nearly 13,000 crude wooden markers that lined the camp’s burial trenches. Today, the Andersonville National Cemetery, which was dedicated in August 1865, bears row after row of alabaster gravestones for Camp Sumter’s victims, including one for its first casualty, Private Swarner.