855 - Bjorn Ironside arrived in France

Claus Deleuran: Viking retreat
France
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 Charles the Bald defeated them at Saltus Particus 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.
Ireland
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.
Wales 
Dubh-Ghenti led by a Norse-Irish chieftain named Orm attacked Gwynedd, only to be repelled by Rhodri Mawr who killed Orm.