In that Epic "The Vikings" Tony Curtis lead the maurauders with a moonstone which was in essence a piece of a meteorite which was magnitized. It pointed north and with a knowledge of the wind and waves it was almost as good as a Garmon!
Appreciated. Interesting story.
Actually it would have pointed to an area in northern Canada as Magnetic North & True North are not the same thing. The differential would have been pretty great for somebody attempting to navigate along the islands of Iceland, Greenland toward Labrador. Still a fixed reference, properly understood, would have helped.