this book articles on many topics related to the relationship between the Vikings and the Rhineland:
on ships and shipping as well as Charlemagne´s maritime defence, historical background information on the socio-economical situation of the Rhineland at the time, but also archeological data on the Viking hoards recently found in the Netherlands and the spectacular remains of a Viking attack on the inperial manor at Zutphen in Holland.
Rudolf Simek