good point but although the western empire fell in 476 the romans left britain starting in about 400 and finished in 410 with honorius letter telling the britains to look to their own defenses.
Thats a decent amount of time to lose the roman art of armorsmithing.
http://www.britannia.com/history/historan.html
almsot every comment listed there mention the 500's not the 9th century.
although most say he never existed at all.