During these years the Vikings made one notable expedition far beyond the ordinary range of their activity. Starting from the Seine in 859 under the leadership of Björn and Hásteinn, they sailed round the Iberian Peninsula through the Straits of Gibraltar. They landed in Morocco and carried off prisoners many of the Moors or 'Blue-men' as they called them. Some of these found their way to Ireland and are mentioned in certain Irish annals of the period. After fresh attacks on Spain they sailed to the Balearic Isles, and Roussillon, which they penetrated as far as Arles-sur-Tech. They wintered in the island of Camargue in the Rhone delta and then raided the old Roman cities of Provence and sailed up the Rhone itself as far as Valence. In the spring of the next year they sailed to Italy. They captured Pisa and Luna (at the mouth of the Magra), the latter being taken by a clever stratagem. Hásteinn feigned himself sick unto death and was baptised by the bishop of Luna during a truce. Then news came that Hásteinn was dead and the Vikings asked Christian burial for him. Permission was given and a mock funeral procession entered the city. It was in reality a band of armed men in disguise and the city was soon captured. The real aim of the Vikings in this campaign was the capture of Rome with its mighty treasures, but, for some reason unknown, they made no advance further south. Scandinavian tradition said it was because they mistook Luna for Rome and thought their work already done! Sailing back through the Straits of Gibraltar they returned to Brittany in 862. The Vikings had now almost encircled Europe with their attacks, for it was in the year 865 that the Swedish Rhôs (Russians) laid siege to Constantinople.
When Alfred secured a definite peace with the Danes in 878, those who were averse to settling permanently returned to their old roving life. They made their way up the Somme and the Scheldt and their progress was not stopped by a brilliant victory gained by the young Lewis III in June 881 at Saucourt, near the Somme, a victory which is celebrated in the famous Ludwigslied. During the same years, another Viking host invaded Saxony winning a decisive victory over Duke Bruno on the Lüneburg Heath. After their defeat at Saucourt the main body of the Danes made their way to Elsloo on the Meuse whence they ravaged the Meuse, Rhine and Moselle districts plundering Cologne, Bonn, Coblentz, Aachen, Trèves and Metz. So alarmed was the emperor Charles the Fat that he entered into negotiations with the Danish king Guðröðr who was with the forces at Elsloo. He secured Guðröðr's acceptance of Christianity and the promise of security from further attack at the price of a large payment of Danegeld and the concession to Guðröðr of the province once held by Hrœrekr, with large additions. The exact extent of the grant is uncertain, but it included the district of Kinnem (round Alkmaar and Haarlem) and probably covered the greater part of Modern Holland from the Vlie to the Scheldt. Here Guðröðr lived in semi-independence and might perhaps have established another Normandy within the empire had he not been ruined by too great ambition. He entirely failed to defend his province from attacks, indeed he probably gave them covert support; he intrigued with Hugo, the bastard son of Lothair II, against the emperor, married his sister Gisla, and then asked for additional territories on the Rhine and the Moselle, on the plea that his own province included no vine-growing districts. Guðröðr had now overstepped all reasonable limits: the emperor entered into negotiations with him but secured his death by treachery when a meeting was arranged near Cleves. With the fall of Guðröðr Danish rule in Frisia came to an end, and though we hear of isolated attacks even during the early years of the 10th century, there was no more serious trouble in that district.
In the autumn of 882, encouraged doubtless by the news of the death of Lewis III, the Danes returned from the Meuse to Flanders and during the next three years ravaged Flanders, Brabant and Picardy, establishing themselves strongly at Louvain. In 885 they abandoned these districts and sailed up the Seine, after a nine years' absence. In November they reached Paris with a fighting force of some 30,000 men and a fleet of 700 vessels. The passage up the river was stopped by fortified bridges and the besiegers were fortunate in having as leaders two men of great ability and courage, first Gauzlin, Abbot of St Germain's, and, later, Count Odo of Paris. The position of Paris was at times desperate. The Danes were exasperated by the stout defence and in their eagerness to plunder further up the river dragged many of their ships some two miles overland past Paris, and so reached the upper waters of the Seine. Later, as the result of peaceful negotiations, they obtained permission to pass the bridges on condition that they only ravaged Burgundy, leaving the Seine and Marne districts untouched; thus had the provinces of the Frankish empire lost all sense of corporate union. The Danes soon made their way as far west as Verdun. Here however they were disastrously defeated by Odo, now king of the West Franks (June 888), and in the next year they finally abandoned the siege of Paris making their way to Brittany.
In Brittany they found another army already busy. The Bretons had won a great victory in the autumn of 888 when only 400 out of some 15,000 Danes made their way back to their fleet. The great here from the Seine now joined forces with the remnants of this army, but proved powerless against Duke Alan, and some returned to Flanders in 890, while Hásteinn with the rest sailed to the Somme. The Danes in Flanders were defeated by Arnulf (afterwards emperor) on the Dyle, near Louvain, in 891, but it had no great effect for soon after we find them again as far east as Bonn. A bad harvest in the summer of 892 brought famine in its train and this was more effective in ridding the land of invaders. In the autumn of the year the whole army, horses and all, crossed in one passage in some 250 ships from Boulogne to the mouth of the Limen in Kent and, shortly after, Hásteinn with a fleet of 80 ships left the Somme and sailed to Milton in North Kent. The story of the campaigns there has already been told. For the first time since 840 the Frankish empire was free from invaders. Grievous as were the losses of the Franks, it is well to remember that those of the Danes had been great also. Their fleet had been reduced from 700 to 250 ships, and as the whole army could still go to England in one crossing, that must also have been reduced from thirty to ten or fifteen thousand men.
When the English invasion had failed, those who could not settle in England returned to their French haunts once more. A small force of eight ships and some 200 men sailed up the Seine under one 'Huncdeus' and gradually their numbers were increased by fresh arrivals from abroad. They made their way north to the Meuse, south to the Loire, and east to Burgundy, but their head quarters were on the lower waters of the Seine. In 903 other invaders appeared on the Loire under leaders named Baret (O.N. Bárðr) and Heric (O.N. Eiríkr). The name of Bárðr is mentioned more than once in the contemporary history of the Norsemen in Ireland, and as the Norsemen were driven from Dublin in 902 it is probable that these invaders came from there. The expedition was not a success and the Vikings soon sailed away again. Of the history of the settlers on the Seine after 900 we unfortunately know practically nothing. The Norman historian Dudo attempted in the 11th century to give a connected account but his narrative is confused and unreliable. Odo was dead and Charles the Simple was more interested in conquering Lorraine than defending Neustria. The clergy were weary of the ceaseless spoiling of the monasteries and anxious for the conversion of the heathen, while the nobles were, as usual, selfish and careless of the interests of the country at large. The Northmen made no great expeditions between 900 and 910, but maintained a steady hold on the Lower Seine and the districts of Bessin and Cotentin. They could not extend their territories and the Franks could not drive them from the Seine. At length, largely through the intervention of the clergy, a meeting was arranged between Charles and the Viking leader Rollo at St Clair-sur-Epte, before the end of 911. Here the province later known as Normandy (including the counties of Rouen, Lisieux, Evreux and the district between the rivers Bresle and Epte and the sea) was given to Rollo and his followers as a beneficium, on condition that he defended the kingdom against attack, and himself accepted Christianity. The Danes now formed a definite part of the Frankish kingdom and occupied a position analogous to that of their countrymen in East Anglia, Northumbria and Mercia in England, except that the latter after a period of freedom had in course of time to pass definitely under English rule.
The story of the foundation of Normandy is obscure: still more obscure is the origin and history of the leader of the Northmen at this time. Norse tradition, as given by Snorri Sturluson, makes Rollo to be one Hrólfr, son of Rögnvaldr earl of Möre, who was exiled by Harold Fairhair and led a Viking life in the west. Norman tradition, as found in Dudo, made him out the son of a great noble in Denmark, who was expelled by the king and later went to England, Frisia and Northern France. Dudo's account of the founding of Normandy is so full of errors clearly proven that little reliance can be placed on his story of the origin of Rollo. The Heimskringla tradition was recorded much later, but is probably more trustworthy, and it would be no strange thing to find a man of Norse birth leading a Danish host. Ragnarr Loðbrók and his sons were Norsemen by family but they appear for the most part as leaders of Danes. How Rollo came to be the leader of the Danes in France and what his previous career had been must remain an unsolved mystery. His name is not mentioned apart from the settlement of Normandy.
The Normans continued to ravage Brittany without any interruption and they were soon granted the further districts of Bayeux, Seez, Avranches and Coutances, which made Brittany and Normandy conterminous.