In July 856 a Viking chieftain named Sidroc entered the River Seine to pillage.
Come winter Sidroc left Frankish waters while Bjørn built a fortified camp on an island called Oscellus, probably Oissel.
The Vikings proceeded to raid as far as Bayeux and Évreux, and the entire region showed little resistance to their movements throughout 857.
)[1] The surviving sources do not record Bjørn's reasons for visiting King Charles at Verberie early in 858.
In the words of the Annales Bertiniani, the preeminent West Frankish annals for the period: “Bjørn, leader of the faction of pirates of the Seine, pursuing King Charles came to the palace in Veberie, and giving him his hands, swore fidelity to him.”[2] Bjørn had probably been offered tribute (danegeld) in return for submitting to the act of commendation (the giving of hands and swearing of fealty).