In order to widen a road in Sweden, archaeologists began excavating a large burial ground — but what they found surprised them. The burial ground in Västmanland had around 100 graves and two burial mounds dating from 600 to 1,000 A.D., archaeologists with Arkeologerna, a part of Sweden’s National Historical Museums agency, said in an Oct. 25 news release.

On one of the burial mounds, archaeologists found three stone tombs, graves added a few centuries after the original mounds. As researchers began excavating these tombs, they noticed two handle-looking shapes sticking out of the rocks. The crusty handles blended in with the light brown rocks nearby, protruding slightly above the boulders and looking distinctively human-made, photos show. As archaeologists carefully excavated the area, they discovered a pair of Viking-age swords, the news release said.

The discovery of the swords was unexpected and highly unusual, according to archaeologists. Only 20 Viking-age swords have ever been found in the region of Västmanland. Excavating the burial ground in Västmanland has been a two-year project that ended with a bang, archaeologists said. Previously, researchers found cremated human and animal bones, game pieces, bear claws, part of a comb, glass beads, arrowheads, parts of horse equipment and a poorly preserved boat grave, according to a description of Arkeologerna’s project. The burial ground was built on top of the remains of an even older farm, likely including the graves of the local Iron Age elites, archaeologists said.