In popular imagination, the Vikings are remembered as fierce warrior seamen who campaigned through Western Europe, terrorizing British, Frankish, and Irish societies. Yet is it possible that the great Viking armies left more in their wake than carnage and destruction? The stories of two families-the Olafssons, who transformed a pirate camp in Ireland into the kingdom of Dublin, and the Haraldssons, whose rule encompassed Hebrides, Galloway, and the...