855 - Bjorn Ironside arrived in France

Claus Deleuran: Viking retreat
A Viking army sailed up the Seine to Pîtres (18 July). He was joined on August 17 by Bjorn Ironside. They looted the Perche region before the Loire Vikings were attacked by a Viking chieftain called Sigtrygg (Sidroc). Sigtrygg had been operating around the Seine and in Ireland, and had in the past sailed with Gudrød. He was now allied with Erispoë, who had paid him to get rid of Hallstein, Gudrød and Åsgeir And defeated them at Saltus articus
The viking army, which had suffered heavy losses in the Loire area, where only 300 vikings survived made a winter camp at a French island in the river, named Jeufosse.
Cerball mac Dunlainge is said to have slaughtered a bunch of Viking intruders, led by Rodolb. In the aftermath of the battle Cerball mac Dunlainge was captured by  Vikings, but he escaped.  Cerball joined a group of Danes led by a chief named Orm in their war with the Norwegians. The Danes might have come from Waterford. People of  Munster begged for Cerball's help against the Vikingsse, and Cerball with the men of Osraige, Horm's Danes and some of the men of Munster inflicted a heavy defeat on the Norwegians.
Dubh-Ghenti led by a Norse-Irish chieftain named Orm attacked Gwynedd, only to be repelled by Rhodri Mawr who killed Orm.