Eleven amputated limbs, two nearly complete skeletons, and scattered artifacts uncovered from a shallow pit at Virginia’s Manassas National Battlefield Park are unearthing rare and grim glimpses of Civil War surgery.

The surgeon’s burial pit is the first of its kind to be discovered at a Civil War battlefield, the National Park Service announced this week.

Experts from the NPS and the Smithsonian Institution have determined that remains date back to August 1862, the time of the Second Battle of Manassas (also referred to as the Second Battle of Bull Run by Union Forces). The pit was likely at the site of a field hospital, set up to tend to the thousands of wounded following the multi-day battle.

Kate D. Sherwood, Smithsonian Institution.

Kate D. Sherwood, Smithsonian Institution.

Kate D. Sherwood, Smithsonian Institution.

NPS Photo/Nathan King

NPS Photo/Nathan King

NPS Photo/Nathan King

Kate D. Sherwood, Smithsonian Institution

NPS Photo/Nathan King

NPS Photo/Nathan King

Kate D. Sherwood, Smithsonian Institution

Kate D. Sherwood, Smithsonian Institution

Kate D. Sherwood, Smithsonian Institution

Kate D. Sherwood, Smithsonian Institution

NPS Photo/Bryan Gorsira

NPS Photo/Bryan Gorsira

The two nearly complete remains likely belonged to Union soldiers who were felled by Confederate bullets. Though they were brought to the field hospital, they died of their wounds without surgical intervention—possibly because they were too far gone—the experts surmised.

Analyses of carbon and oxygen isotopes in their bones revealed that they both ate food and drank water from northern latitudes growing up. They were also found alongside buttons from a Union sack coat.

Based on teeth, joints, and bone structure, the first man was likely between 25 and 29 years of age when he was shot in the right buttocks. The .577 Enfield bullet—used mainly by the Confederate Army during the Second Manassas—was still lodged in his right femur. The second man was likely between 30 and 34 years of age and died from a .31 caliber lead buckshot to the upper arm, pelvis, and leg.

The eleven arms and legs are still undergoing research at a laboratory at the Smithsonian’s National Museum of Natural History. Archeologists there are analyzing the etchings on the bones to determine the skill and technique of the surgeons during the amputations. From the clean saw marks, experts can determine the position of the limbs during amputation, the speed of cutting, and the number of strokes it took to clear each one.

With no antibiotics and limited anesthetics and precision surgical techniques, surgeons commonly turned to amputations during the Civil War. Experts estimate that there were approximately 60,000 amputations during the war and that these surgeries made up around three-quarters of all combat-related surgeries.

Historians at the Smithsonian plan to use medical records from the time to try to match the limbs in the pit with the soldiers they came from. If they can determine that, they may be able to trace the soldiers to see how they fared after their amputations. In the meantime, the NPS has transferred the full remains of the two Union soldiers to the Army, who will inter them at Arlington National Cemetery.

The Second Battle of Manassas, like the first, was a Confederate victory. The battle occurred over August 28-30 and claimed an estimated 22,000 casualties, nearly 14,000 on the Union side and more than 8,000 on the Confederate side.

The Park Service stumbled upon the pit in 2014 during a utility project and began excavating it in 2015. It has been quietly studying the trove of bones and artifacts since.