The first Normans were Rollo and his fellow Vikings, marauders from the north, who fashioned the county (later the Duchy) of Normandy from lands won at the mouth of the Seine in about 911, making Rouen their capital. The heirs of these pagan Northmen contrived a brilliant transformation of themselves into Christian warriors, and went on to conquer England, southern Italy and Sicily, and even distant Antioch, in the process carving out a dynamic reputation throughout Western Europe and the Mediterranean. Norman princes encouraged the celebration of these remarkable achievements in histories...