The Last Viking
By Poul Anderson
Harald Hardrede, last and greatest of the Norse kings, matures from an uncrowned young man hungry for battle to a ruler with dreams of expansion he is determined to realize.
The Golden Horn: Only seventeen, Harald Sigurdharson—one day to be called Hardrede—covets the throne he is still too young to take. Restless, the warrior journeys to Constantinople where he becomes a member of the fabled Varangian Guard entrusted with the safety of the Byzantine emperor and romances an enticing beauty from a powerful clan.
Poul William Anderson was an American science fiction author who began his career during one of the Golden Ages of the genre and continued to write and remain popular into the 21st century. Anderson also authored several works of fantasy, historical novels, and a prodigious number of short stories. He received numerous awards for his writing, including seven Hugo Awards and three Nebula Awards.
Used, very good. 1980 Zebra Books, first edition.