Yes, it seems well documented. Apparantly they raided paris as well? Literally sailed to France and then up the Seine river to Paris. The raids seem to have been inspired by the death of the Holy Roman Emperor Charlemagne. So there was something going on there. Also
Charlemagne spent the greater part of his reign in military conquest, consolidating his power and that of the church. His campaigns against the people of Saxony were especially brutal and epitomized by the Massacre of Verden in 782 CE when he had 4,200 Saxons executed