Normandy takes its name from the Viking invaders who menaced large parts of Europe towards the end of the 1st millennium in two phases (790–930, then 980–1030). They were called Nortmanni in the Medieval Latin documents, which means “men of the North”. This name provides the etymological basis for the modern term “Norman” and “Normandy”,
The first Viking raids began between 790 and 800 on the coasts of western France. Several coastal areas were lost during the reign of Louis the Pious (814–840). The incursions in 841 caused severe damage to Rouen and Jumièges. The Vikings attackers sought to capture the treasures stored at monasteries, easy prey considering the helplessness of the monks to defend themselves. An expedition in 845 went up the Seine and reached Paris. The raids were carried out primarily in the summer, the Vikings spending the winter in Scandinavia.
After 851 they began to stay in the lower Seine valley for the winter. In January 852 they burned the Abbey of Fontenelle. Over the next few years they continued to raid along the coast and down the Seine even as far as Paris.
After being defeated by the Franks in the Battle of Chartres, in 911, the Viking leader Rollo and the Frankish King Charles the Simple signed the Treaty of Saint-Clair-sur-Epte, under which Charles gave Rouen and the area of present-day Upper Normandy to Rollo, establishing the Duchy of Normandy. In exchange Rollo pledged vassalage to Charles and agreed to be baptized. Rollo vowed to guard the estuaries of the Seine from further Viking attacks.
With a series of conquests, the territory of Normandy gradually expanded. While many buildings were pillaged, burned, or destroyed by the Viking raids, it is likely that the picture given by ecclesiastical sources is unfairly negative: no city was completely destroyed. On the other hand many monasteries were pillaged and all the abbeys were destroyed. Nevertheless, the activities of Rollo and his successors had the effect of bringing about rapid recovery.
The Scandinavian colonisation was principally Danish, with a Norwegian element. A few Swedes were maybe present. The Viking colonisation was not a mass phenomenon. Nevertheless, in some areas the Scandinavians established themselves rather densely. In fact, the Nordic settlements in Normandy can be qualified as Anglo-Scandinavian, because most of the colonists must have come after 911 as fishermen and farmers from the English danelaw and a consequent Anglo-Saxon influence can be detected.
The merging of the Scandinavian and native elements contributed to the creation of one of the most powerful feudal states of Western Europe. The naval ability of the Normans would also eventually allow them to conquer England.