Archaeologists found the coin on Monday at a site on the island of Öland that's been compared to Italy's Pompeii.
A small team of archaeologists at Kalmar County museum, in collaboration with Lund University, has been digging at the site for the past three years. The team is studying the Migration Period in Scandinavian history, from about 400 to 550 AD, centuries before the Viking Age.
While the team has found several hundred of the coin already, Monday's discovery was a big one, said archaeologist and project manager Helena Victor.
"This is the first one found in an archaeological context," she told The Local. "Normally we find them while we're plowing the field. But we found this one inside a house where we found people who'd been killed."
The object, a small golden coin also known as a solidus, is from the Roman Empire and may be an important puzzle piece in mapping the island's history.