(CNN) Never heard of a "witch bottle"? Step right in, friend, sit a spell (not the evil kind) and we'll tell you why archaeologists believe a broken bottle found in Virginia just might be one.

Back in the day (beginning around the Middle Ages), people in the British Isles and elsewhere would try to ward off evil spirits by filling jugs or other containers with bent pins, hair, urine, nail clippings or other items. The idea was the contents would draw in and trap a harmful spirit. The witch bottle tradition came to the US and was still in play in the mid-19th century, during the Civil War.

Fast forward to 2016, when the William & Mary Center for Archaeological Research took part in a dig ahead of a widening project on Interstate 64 near Williamsburg.

A crew found a green bottle next to the remains of a hearth built by Union troops between 1862 and 1865 at Redoubt 9, one of a string of mini-fortifications erected by Confederates, but later occupied by Federal troops. The remains of the redoubt are in the interstate's median.

Inside the Civil War-era bottle, according to Joe Jones, director of the center, was a knot of iron nails that had "corroded into a ball." The neck of the bottle had cracked, probably because of the weight of accumulated soil since the war. The broken top remained in place.

At first glance, one might think a soldier had downed the contents of the bottle, perhaps containing beer or soda, and used it to hold the square nails.

But archaeologists wondered whether the jug might, in fact, have been used as a witch bottle.

There was plenty to be afraid of, after all. The 5th Pennsylvania Cavalry Regiment and other units would man the forts whenever new threats came from Confederate troops. They dodged the occasional bullet and built new levels of the fort to better protect themselves and improve their line of fire. Often, they simply built over the existing levels of the redoubt.

"Witch bottles are the type of things people would use more generally in famine, political strife or feeling under threat," said Jones. "The Union troops were definitely under all those kinds of existential threats or fears."

Officials stress the witch bottle scenario is a theory. Because of the crack, any other items beyond the nails -- possibly urine -- evaporated or disappeared. "It would be pointless to do the type of analysis one might do if the bottled had been capped and intact," the center's director said.

So, while the true story may never be known, Jones believes the war environment, the existence of the nails and the placement of the bottle make it likely the bottle was used as a talisman.

Colleagues Oliver Mueller-Heubach and Robert Hunter approached him about the possibility.

The fact that it was found near a hearth in the fort's officers area makes a strong case for the use as a witch bottle, says Jones. Research has indicated placement of bottles near hearths and chimneys was commonly used in the process of warding off witches or breaking a spell.

"They are placed near a hearth so the heat of the fire heats the nails, which helps trap and hold evil spirits," he said. While about 200 witch bottles have been found in Great Britain, fewer than a dozen are known in the US, according to an article in Historical Archaeology.

A fanciful depiction of the 1862 Battle of Williamsburg. The Union occupied the area afterward.

In a press release this week about the discovery, Jones said an officer leading Union troops might have had another use for the bottle than to just hold nails.

"Given the perceived threat of Confederate attack and general hostility of local residents, he had good reason to pull all the stops and rely on folk traditions from his community in Pennsylvania to help protect his temporary home away from home."

Jones said archaeologists found no evidence of pre-Civil War occupation of the site.

Besides the bottle -- which was made in Pennsylvania between 1840 and 1860 -- archaeologists recovered a wealth of artifacts at the site: Canteen fragments, bullets, horseshoe nails, uniform buttons and ink bottle fragments, among others.

But perhaps the most tantalizing and most mysterious is the bottle, which is being stored with other artifacts for further research. The bottle is marked, "Charles Grove of Columbia, PA."

For his part, Jones said he is convinced the container is a witch bottle.

"I think it is a manifestation of that folk practice," he said. "It is important to let people know about that."

Clarification: This story has been updated to provide more detail on the positioning of the bottle pieces.