Mowat's premise is that Iceland, Greenland and North America were visited and settled before the Vikings by Europeans from the northern British Isles.
Mowat believes that the Albans were hunters of walrus ivory[REF] and it was the demand for this valuable material,[REF] that lead the Albans to discover Iceland or Thule centuries before the Vikings (As described by the Greek explorer Pytheas in 330 BC.)[REF]