A good few years ago I studied archaeology of South East England, which was a very fluid definition as for Prehistory it included Stonehenge and for Post Roman it included South Cadbury. This part of it electrified me: scores of Iron Age hillforts all over the South West refortified in the late 5th century, and new walls and gate built at South Cadbury by a proper Roman trained military engineer nearly a century after the Roman army left Britain.
Naturally, that set me wondering who this man was, and I came up with a hypothesis that, being intellectually more honest than some writers, I felt I could only deal with in fiction ... which is what I have been doing: I've nearly got him there, and the succeeding books are plotted out and started, but it's been a long slog.
In the course of researching it, I found out far more about the so-called Dark Ages than I ever dreamed existing, to the point that I get very emphatic about using the term "Late Antiquity" instead.
I also discovered some very interesting facts about the time around 500. As I mentioned in a comment recently, something very major happened at that date, but it's a bit more peculiar than it looks at first sight.
To start with, most of the late 5th century defences face west, not east - i.e. against the Irish raiders, rather than the Saxons. That's the way South Cadbury faces; that's the direction the beacon on Glastonbury is concerned with. It looks as if that was a very long drawn out campaign, with the battles against Aelle being a short interlude (and a very successful one) followed by a return to focussing on the west.
The other thing I discovered was what an appalling danger Aelle was. To start with he had other kings under him; whatever the precise meaning and derivation of "Bretwalda" this is clearly the case. And secondly, he did something no other barbarian managed to do - not even the Huns: he took a Roman fortified place. Throughout Europe, if people could get behind walls, they were safe. Even Theodoric only defeated Odovacer by reaching a stalemate and offering a peace deal that he betrayed; he couldn't take Ravenna, which was a walled town, not a specially constructed fort. The fact that Aelle took Anderida marked him out as potentially the most dangerous leader in Late Antiquity, certainly since Alaric (and he doesn't count as a barbarian for these purposes - he was a Roman-paid officer who got annoyed when he wasn't given Roman troops to command so didn't have access to the State-run arms factories).
I'll come back some time to who the leader who defeated Aelle was, but if he defeated the greatest barbarian leader, possibly including Attila, he must have been supremely great.
(And, of course, he had a good military engineer!)