books.google.de - The collapse of Roman rule in Britain was not so much a sudden catastrophe as a long and drawn-out decline. The 'Celtic' Britons retreated gradually to the highland areas of Wales, Cornwall and the south-west of Scotland. Control of the fertile eastern lowlands was lost to warriors of Germanic origin...http://books.google.de/books/about/Anglo_Saxon_Thegn_AD_449_1066.html?hl=de&id=fXrOd03NWykC&utm_source=gb-gplus-shareAnglo-Saxon Thegn AD 449-1066
