857 - Dorestad and Utrecht plundered

Denmark
Rurik arrived in Denmark with Godfred, son of Harald Klak. They had earlier made claims on part of the kingdom, but have been rejected. Rurik then negotiated that the Danish king had to give up some areas by the Eider.
Claus Deleuran: Vikings in Paris
France
Vikings entered Paris and plundered and burned a few churches and received a ransom from other churches.Tours was attacked and the town Poitiers was destroyed in a joint attack with Pepin of Aquitaine(Sonson of emperor Louis)
Frisia
Later that year Dorestad and Utrecht was plundered. Both these towns was part of Ruriks area and the attacks possible had a connection to the incidents in Denmark.
Ireland
Olav the White and Ivar the Boneless repelled an attack on Munster by Gall-Gaedhil commanded by Kjetil Flatnose leadership. Kjetil Flatnose