Conversation so far:
where is the castle in the vikings film
Aella's castle in the film, The Vikings, was the real Fort de la Latte in north east Brittany in France
who directed the film, the vikings
The Vikings was directed by Richard Fleischer
was the film the vikings based on a novel
The Vikings was based on the 1951 novel The Viking by Edison Marshall

Question: what was the novel based on
Self-contained rewrite: what was the novel the viking based on