Paris was finally secured against Scandinavian attack by the establishment of the Duchy of Normandy. By the treaty of Clair-on-Epte in 913, Rolf Ganger, changed in French and Latin mouths into Rou and Rollo, became the man of the King of Laon for lands which were taken away from the dominion of the Duke of Paris. Charles the Simple, the restored Karling, was now King; Robert, the brother of Odo, was Duke of the French, and there can be no doubt that the tottering monarchy of Laon gained much by the dismemberment of the Parisian Duchy and by the establishment at the mouth of the Seine of a vassal bound by special ties to the King himself. The foundation of the Rouen Duchy at once secured Paris against all assaults of mere heathen pirates. France had now a neighbour to the immediate north of her--a neighbour who shut her off from the sea and from the mouth of her own great river--a neighbour with whom she might have her wars, as with other neighbours--but a neighbour who had embraced her creed, who was speedily adopting her language and manners, and who formed, part of the same general political system as herself. The shifting relations between France and Normandy during the tenth and eleventh centuries form no part of our subject, but it will be well to bear in mind that Paris was at once sheltered and imprisoned through the Norman possession of the lower course of the Seine. It follows then that the next besiegers of Paris came from a different quarter; and these next besiegers came from the quarter from which its last besiegers have come. In the course of the tenth century, the century of so many shifting relations between Rouen, Laon, and Paris, while the rivalry between King and Duke sometimes broke forth and sometimes slumbered, Paris was twice attacked or threatened by German armies. Both the First and the Second Otto at least appeared in the near neighbourhood of the city. In 946, the first and greatest of the name, not yet Emperor in formal rank, but already exercising an Imperial pre-eminence over the kingdoms into which the Frankish Empire had split up, entered the French Duchy with two royal allies or vassals in his train. One was the Burgundian King Conrad, Lord of the realm between the Rhone and the Alps; the other was the nominal King of Paris and its Duke, Lewis, alike the heir of all the Karlings and the descendant of our own Ælfred, whose nominal reign over the Western Kingdom was practically well nigh confined to the single fortress of Compiègne. Among the shifting relations of the Princes of the Western Kingdom, Hugh the Duke of the French and Richard the Duke of the Normans were now allied against their Carolingian over-lord. He had lately been their prisoner, and had been restored to freedom and kingship only by the surrender of the cherished possession of his race, the hill and tower of Laon. Otto, the mighty Lord of the Eastern realm, felt himself called on