Recommended reading: Eaters of the Dead, by Michael Crichton (1976):

Eaters of the Dead

Full title:

Eaters of the Dead: The Manuscript of Ibn Fadlan Relating His Experiences with the Northmen in AD 922

By Michael Crichton.

Filmed as The 13th Warrior (1999), directed by John McTiernan.

Mass Market Paperback.
Published by Harper.
First published 1976.
ISBN 13: 9780061782633
ISBN 10: 0061782637
ASIN: 0061782637

Description:

The year is A.D. 922.  A refined Arab courtier, representative of the powerful Caliph of Baghdad, encounters a party of Viking warriors who are journeying to the barbaric North. He is appalled by their Viking customs — the wanton sexuality of their pale, angular women, their disregard for cleanliness . . . their cold-blooded human sacrifices. But it is not until they reach the depths of the Northland that the courtier learns the horrifying and inescapable truth: He has been enlisted by these savage, inscrutable warriors to help combat a terror that plagues them — a monstrosity that emerges under cover of night to slaughter the Vikings and devour their flesh . . .