For 1000 years, from the 4th century onwards, the Norse people of Scandanavia carved magical symbols known as runes on wood and stone. One such rune called Valknutr or Walknot, the sign of the slain, is a triangular representation of the Borromean Rings. This rune has been found on an early English ring, and also on the woodcarvings and tapestry of the Oseberg ship burial. The Walknot is also found on the picture-stones of Gotland, an island in the Baltic sea off the southeast coast of Sweden. A picture-stone showing the Walknot, reproduced here, depicts a human sacrifice to Odin.

The Borromean Rings is a link of three rings that, although no two rings are linked, cannot be separated without cutting one of the rings. If any one of the rings were removed all three would separate. The Borromean Rings get their name from the Italian Borromeo family whose coat of arms bore such a device. The correspondence between the Walknot and the Borromean Rings was pointed out by Peter Cromwell in The Mathematical Intelligencer, Winter 1995, Vol 17, No. 1.