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 .