The premise is that the tribal groups within Roman Britain were much more differentiated than most histories assume, and that they were never effectively submerged into a coherent Roman province. Even in the second and third centuries, he thinks there was a lot more intertribal raiding even in Southern England than is documented. In particular he thinks the Iceni came West to raid the Catuvellauni (around London and the Southeast) and the Brigantes (biggest tribe in Britain, remember) regularly came charging South to loot Corieltauvi land around Leicestershire from about 140AD onwards.
His reasoning for this is that in the second half of the second century, a number of villas are torched in what we think might be Catuvellauni and Corieltauvi land (he seems rather confident about exactly where these lie: unless I've missed something, he's basing that on a fairly small number of pre-conquest coin finds, which does seem a small basis for quite a big theory). Also, there are a lot of town walls going up, around quite small towns in Southern England - why did they need those? And concentrations of a particular style of brooch (the 'crossbow brooch') which are thought to be only worn by the military in those same towns - all suggesting that those towns had something real to defend against, which isnt' recorded in the historical texts.
(This is excellent news for the story about Isca D., if I ever manage to finish the dratted thing, given that I have given it a military commander and auxiliary garrison, in what I was worried up to now might be an ahistorical manner. )
I knew, but hadn't really processed, that around 140AD was when the new Governer Urbicus moved troops North of Hadrian's wall, took Valentia, and then started building the Antonine Wall at the top of it.
Laycock thinks that this was because Hadrian's Wall, going right through Northern Brigantes territory, had proved to be a really difficult line to hold when regularly raided from the South. He thinks the Brigantes voiced their complaints about being cleft in twain so forceably that it was decided to move the whole border North so that all the Brigantes would be inside, but happy and prosperous, rather than being divided and both parts being annoyed about it.
This is an intriguing theory. He bases it partly on the modern experience of UN intervention in small messy local wars in Bosnia and Serbia. I'm not entirely sure whether that's a good parallel or not - I can certainly see that, as he says, the Roman experience is Not Like WWII. But I'm not sure if it would be that much like a modern attempted-peacekeeping mission either, and it seems to involve a phenomenal amount of building. Hmm.
From my selfish viewpoint, having written about half a story about one member of the Brigantes and one member of the Iceni wandering round Dumnonia, I now need to at least work out what I think the reaction to the 140AD invasion of Valentia would be, and possibly think about implications of renewed Iceni raiding as well. Hm. I'm *never* going to finish writing this am I... ?