Within the next few years, they established themselves in strong posts at Oissel, above Rouen, and at Melun, above Paris. The greater part of the last sixteen years of Charles the Bald (_d._ 877) was occupied in defending Paris against their annual forays, repairing the bridges they had destroyed, and so cutting off their return from expeditions up the Marne and Oise. But, although they were constantly checked, they always returned. They abandoned the siege of Paris in 885-6, but only after Charles the Fat had paid them off. The last great invasion of France by the Northmen was in 911, when, by the treaty of Saint-Clair-sur-Epte, Charles the Simple ceded the duchy of Normandy to Rollo. The actual settlement of the Northmen in England began in 851, eight years after the occupation of Noirmoutier. They wintered in Thanet, and sailed thence up the Stour and Thames, taking Canterbury and London. As in France, their landward excursions from their boats were less successful, and they were seriously beaten by Æthelwulf at Ockley in Surrey. But failure did not hinder them from returning. As in France, the system of buying off their attacks was adopted—a ready inducement to repeated plunder. In 887 they were in the Humber, and dealt a final blow to the decaying power of Northumbria at York. Next year they invaded Mercia up the Trent, and established themselves at Nottingham. The years 870 and 871 were remarkable for their land operations. The defeat of the East Anglian king Edmund in Suffolk laid Mercia and Lindsey open to their ravages, and so established their power in what was to become the Danelaw; while in 871, within reach of the Danish camp on the Thames at Reading, occurred the great series of battles in Berkshire and Wiltshire, in which Alfred’s bravery was proved. The details of Alfred’s defence of Wessex against the Northmen are well known: the compromise effected at Wedmore in 878 preserved the south of England to Englishmen, but established the Danes north of a line which may roughly be represented by the course of the Welland, Soar, upper Trent, and Mersey. England, however, had to endure a long intestine warfare for years after the death of Alfred. The strenuous efforts of his children, Edward the Elder and Æthelflæd, prevented the men of the Danelaw from extending their power southwards. But the Northmen used persevering tactics, and not merely the enemy within, but fresh invasions from without, disturbed the peace of the monarchs of Wessex during the later part of the tenth century. After the disastrous reign of Ethelred the Redeless came a period of Danish rule over the whole of England; while the reigns of the last Saxon kings formed the prelude to the final invasion of the Northmen, the Norman conquest.