A medieval Viking sword fragment unearthed in Friesland is unique for the Netherlands and one of only two such fragments ever found, the Fries Museum has said.

The 10th-century copper pommel cap, which is adorned with animal heads and which experts think may have been gilded, was found in a field in Witmarsum in May.

Sander Visser was just about to head home after a disappointing day when his metal detector started beeping. “All of a sudden, bang, a loud tone. 95 times out of 100 it’s a piece of rubbish but you never know,” he told broadcaster NOS.

Visser found the pommel at a depth of 20 centimetres and knew right away he had something special. “I knew this wasn’t just a lump of scrap metal, the shape of the animal heads was very clear. I knew it was a sword pommel but I had no idea it belonged to a Viking sword,” he said.

Diana Spiekhout, a curator at the Fries Museum, is making an inventory of swords found in what was medieval Frisia, which included the Dutch coastal areas. She said the piece is an important link between the Frisian world and the Vikings and will provide insights into the role of weapons in northwestern Europe.

The specific decoration of the pommel shows that swords were invested with human characteristics, she said, much like Excalibur, the sword from the Arthur legends.

“They had an important symbolic value and would have been costly, particularly if they had shown their mettle in battle. Swords often went down the generations, or were gifts from one leader to another,” she said.

It is unlikely the rest of the sword is still in the ground, although archeologists will go back to search the field. “We think the sword was “scalped” at some point. Maybe someone altered it or captured it. There are lots of scenarios,” Spiekhout said.

Visser, who was given a bronze replica of the pommel, has become a Viking fan since his find. “I have seen a lot of films and pay close attention to the swords”, he said.

The pommel will be exhibited at the Archeological Museum in Leiden and will then go to its permanent home in the Fries Museum in Leeuwarden.