Danskebjerge The remains of the ring fortress of Vallø Borgring in Denmark. Archaeologists believe they have uncovered evidence of ancient arson at the site.

It's one of the coldest cases of all.

Police in Denmark have been called to Vallø Borgring, the remains of a Viking fortress, over evidence of arson committed more than 1,000 years ago.

"All indications are that there has been a fire set at the gates of the castle," said archaeologist Jens Ulriksen, who is leading the excavation of the fortress, according to Copenhagen Post. "The outer posts of the east gate are completely charred, and there are signs of burning on the inside."

The ring fortress is the last to have been built by King Harald Bluetooth, who ruled from the mid- to late-900s, according to Archaeology Today.

We're proud to host a talk on the Vallø Borgring with the team behind the huge discovery. http://t.co/7TNJwM3BoW pic.twitter.com/FeBnq2tOhm — JORVIK Viking Centre (@JorvikViking) January 16, 2015

“Our theory right now is that other powerful men in the country attacked the castle and set fire to the gates,” Ulriksen was quoted as saying.

The newspaper reports that archaeologists have asked police to provide a fire safety investigator as well as dogs.

"Hopefully, they can say more about how the fire was started," Sanne Jakobsen, communications manager at Southeast Museum Denmark, told Danish Radio, according to a translation from Sputnik. "We generally have good experience of cooperation with the police. For instance, we have previously used their sniffing dogs to dig out bones from the earth."

danefromspain via Getty Images A runestone ordered built by King Harald Bluetooth. New evidence shows a fire at one of his castles may have been an act of arson.

The ancient king's name got a new life in recent years as it was used for the modern Bluetooth standard.

As Harald Bluetooth united Denmark, the bluetooth standard united different devices from different manufacturers, Jim Kardach, one of the founders of Bluetooth SIG, wrote 2008.

The symbol for Bluetooth is based on a combination of two runes.

1,000-Year-Old Viking Ruler Harald Bluetooth on Trial in Denmark - https://t.co/3UkaXZs2OE



... pic.twitter.com/Ng3icJi6Zq — VeteransTodayNetwork (@veteranstoday) July 1, 2016