Original: Charlemagne and the Avars Birka, Sweden Biskupin, Poland Calleva Atrebatum, Silchester, England - Large Romano-British walled city 10 miles south of present day Reading, Berkshire.
Simplified: Birka, Sweden Biskupin, Poland Calleva Atrebatum,Silchester,England ,UK - Large Romano-British walled city 10 miles south of present day Reading.