Below are a few passages taken from the Annals of St. Bertin, which show something of the character of the Northmen's part in early French history. St. Bertin was an abbey in France. This account was probably written by a group of monks living there.
From The Annals of St. Bertin,
Summarize the events in this section
843 A.D. Pirates of the Northmen's race came to Nantes, killed the bishop and many of the clergy and laymen, both men and women, and pillaged the city. Thence they set out to plunder the lands of lower Aquitaine. At length they arrived at a certain island [the isle of Rhé, near La Rochelle, north of the mouth of the Garonne], and carried materials thither from the mainland to build themselves houses; and they settled there for the winter, as if that were to be their permanent dwelling-place.
844. The Northmen ascended the Garonne as far as Toulouse and pillaged the lands along both banks with impunity. Some, after leaving this region went into Galicia [in Northern Spain] and perished, part of them by the attacks of the crossbowmen who had come to resist them, part by being overwhelmed by a storm at sea. But others of them went farther into Spain and engaged in long and desperate combats with the Saracens; defeated in the end, they withdrew.
845. then the other, came without meeting any resistance to Paris. Charles [the Bald] resolved to hold out against them; but seeing the impossibility of gaining a victory, he made with them a certain agreement and by a gift of 7,000 livres he bought them off from advancing farther and persuaded them to return. Euric, king of the Northmen, advanced, with six hundred vessels, along the course of the River Elbe to attack Louis of Germany. The Saxons prepared to meet him, gave battle, and with the aid of our Lord Jesus Christ won the victory. The Northmen returned down the Seine and coming to the ocean pillaged, destroyed, and burned all the regions along the coast.
846. The Danish pirates landed in Frisia. They were able to force from the people whatever contributions they wished and, being victors in battle, they remained masters of almost the entire province.
847. The Northmen made their appearance in the part of Gaul inhabited by the Britons and won three victories. Noménoé [a chief of the Britons], although defeated, at length succeeded in buying them off with presents and getting them out of his country.
853-854. The Danish pirates, making their way into the country eastward from the city of Nantes, arrived without opposition, November Eighth, before Tours. This they burned, together with the church of St. Martin and the neighboring places. But that incursion had been foreseen with certainty and the body of St. Martin had been removed to Cormery, a monastery of that church, and from there to the city of Orleans. The pirates went on to the château of Blois and burned it, proposing then to proceed to Orleans and destroy that city in the same fashion. But Agius, bishop of Orleans, and Burchard, bishop of Chartres, had gathered soldiers and ships to meet them; so they abandoned their design and returned to the lower Loire, though the following year  they ascended it anew to the city of Angers.
855. They left their ships behind and undertook to go overland to the city of Poitiers; but the Aquitanians came to meet them and defeated them, so that not more than 300 escaped.
856. On the eighteenth of April, the Danish pirates came to the city of Orleans, pillaged it, and went away without meeting opposition. Other Danish pirates came into the Seine about the middle of August and, after plundering and ruining the towns on the two banks of the river, and even the monasteries and villages farther back, came to a well located place near the Seine called Jeufosse, and, there quietly passed the winter