Over the course of the Viking Age, virtually all of Europe’s western seaboard, and countless towns along the major rivers that led into the Continent, were plundered by the Vikings.
Viking raids on the Frankish Empire began in earnest in 820, and by 834, attacks became a regular occurrence for a generation. The Vikings plundered seemingly every city and town in the Frankish Empire that they could reach, including such centers as Rouen, Quentovic, and Nantes. In 843, they overwintered on the mainland for the first time. Paris was sacked on Easter Sunday of 845, and the Franks were obligated to pay the Vikings a hefty ransom for them to leave. A Frankish monk gave the following account in the 860s:
The number of ships grows: the endless stream of Vikings never ceases to increase. Everywhere the Christians are victims of massacres, burnings, plunderings: the Vikings conquer all in their path, and no one resists them: they seize Bordeaux, Périgeux, Limoges, Angoulême and Toulouse. Angers, Tours, and Orléans are annihilated and an innumerable fleet sails up the Seine and the evil grows in the whole region. Rouen is laid waste, plundered and burned: Paris, Beauvais and Meaux taken, Melun’s strong fortress leveled to the ground, Chartres occupied, Evreux and Bayeux plundered, and every town besieged.
As Viking raids became more common, local kingdoms turned to granting lands at the mouths of rivers to Norse chieftains in exchange for protecting them and becoming Christians. The Frankish region of Normandy was given to the Viking chieftain Rollo in exchange for his protection of the Franks. A similar arrangement was made with the Danes Harald and Rorik with Walcheren, an island in Frisia. They became assimilated into Frankish culture.
In 859, a Viking fleet led by Björn “Ironside” (Jarnsiða) and Hastein set out for the Mediterranean, where for three years they raided Spain, Italy, the Rhône valley, and North Africa. Their fortunes waxed and waned dramatically during that time. By 862, after many raids and battles, only a third of the ships and crew that had set out in 859 returned, but those who did return were massively rich. The Vikings returned to Spain to raid in the mid-tenth century, but this time with mixed success.