In late August of 1862, the second year of the American Civil War, a large Union army led by Major General John Pope was camped near a tributary of the Potomac River in Manassas, northern Virginia, when they were attacked by Confederate forces commanded by Stonewall Jackson. The ensuing two-day clash, named the Second Battle of Bull Run or Second Battle of Manassas, left an estimated 1,305 Confederate and 1,716 Union men dead, with many thousands more captured or wounded on each side.

Now, more than 150 years later, we are gaining fresh insight into the surgical techniques that army doctors employed to treat the multitudes of severely injured soldiers, such as those at Bull Run, while bullets and cannonballs were still flying nearby.

As reported by the National Park Service (NPS) this week, a burial pit containing two near-complete skeletons and a jumble of 11 arms and legs has spurred a whirlwind of research since it was first discovered, unexpectedly, at the site of the conflict in 2014.

The findings are the only known examples of Civil War surgical remains, according to the NPS and Smithsonian Institute archaeologists in charge of the investigation. After a careful excavation, the stash of bones and surrounding material were relocated from the Manassas National Battlefield Park to the Smithsonian’s state-of-the-art National Museum of Natural History laboratory for thorough physical and chemical analyses.

Radioisotopes within the two skeletons revealed that the individuals grew up in northern latitudes, which, combined with the coat buttons uncovered next to them, points to the men being Union soldiers. The bone structure and condition of the teeth and joints suggests that the first skeleton belongs to a man in his late twenties. His cause of death was easy to determine: a .577 Enfield bullet – the type favored by the Confederate army – remained lodged in his femur.

The other skeleton is believed to have been between 30 and 34 years old and seems to have died from the blast of a .31 caliber buckshot that struck his upper arm, pelvis, and leg.

It appears that both men were brought to the field hospital but not operated on because their wounds were either too severe or they died before the doctor could get to them. On June 19, 2018, the remains were transferred to the US Army, who plan on interring them at Arlington National Cemetery.

Study of the assorted arms and legs is ongoing. The NPS notes that examination of the cut marks on the bones will determine how the surgeon held the saw and can even indicate how skilled they were at removing damaged limbs. It is estimated that about 60,000 surgeries were performed during the civil war; two-thirds of these were amputations. Anesthesia, discovered just 16 years prior, was often unavailable, and the risk of death from subsequent infection – this was the tail end of the pre-antibiotic era – was very high.