Poul Anderson 
Golden Slave 

100 B.C. The Cimbrian hordes galloped across the dawn of history and clashed in screaming battle against the mighty Roman legions. Eodan, son of Chief Boierek, has been on the war campaign for many years. The Cimbrain army has become a hungry homeless pagan tribe. Their sworn enemy, the Romans, they have battled against gloriously. But for all the burning towns, the new-caught women weeping, the wine drunk, the gold lifted, the Cimbri did not find a home. Eodan, the proud young chieftain, had been caught and sold into slavery, his infant son murdered and his beautiful wife, Hwicca, taken as a concubine. But the whips and slave chains could not break the spirit of this fiery pagan giant who fought, seduced and connived his way to a perilous freedom to rescue the woman he loved. A struggle that would make him a lover, pirate, commander, and in the end the struggle would make him a legend! (Goodreads)