The 535 event could have been, in part, due to eruptions in Iceland that spewed hydrofluoric acid across Europe.Those kind of speculations are really interesting. Could change our understanding of history.
What if no one had any particular interest in attacking Rome but some cataclysmic event set in motion some chain of events?
http://www.britannia.com/history/docs/annales.html I like this reference to 540 AD. You have Arthur and Modred both dying. No doubt the spirits of the wells of inspired storytelling fled ~ as real life became something truly incredible. And then: an.’ 548 Mortalitas magna in qua pausat mailcun rex genedotę.