For some three and a half centuries Viking sea-raiders from Scandinavia terrorized the people of western Europe.
At first they came as plunderers, then as settlers and traders, but always they were fierce and dangerous.
Their light dragon ships were equally at home in the North Sea and in the river estuaries which led them inland to seize strong-points, from which they fanned out over the countryside.
Early in the 10th century, one of these war-bands, led by a certain Rollo captured the town of Rouen on the River Seine, and secured a grant of territory from the then king of the Franks.
Rollo and his descendants as cunning as they were formidable, imposing their power equally on Frankish natives and fresh waves of Vikings, so that by the early 11th century they ruled a vast tract which had come to be called terra Normannorum, the land of the men from the north.
Rollo's great-grandson, Richard II (996-1026), was the first regularly to call himself "Duke of the Normans".
By then the little state was prosperous and strong, enjoying a rich agriculture and a vigorous commercial life focused on the capital, Rouen.