[David Wilson]

Well, if you want to get nit-picky about it, Scotland is part of Britain (Great Britain is the whole island).....

"Briton" is not really a specific tribe, but a generic sort of word for the inhabitants of Britannia. They would have been related to their northern neighbors, those guys known as the Picts (the Romans called that part of Britain "Caledonia"). Language and culture would have been fairly similar, although there's little actual evidence of this.

True, the Gaelic-speakers were still in Ireland at this time, although trade and other cultural connections certainly existed between the Irish and the various peoples of Britain -- especially in the Islands and West Highlands (eventually, of course, those Irish moved on in and took over the place... and that's where the Scots come from).

As to the accuracy of the movie, from the trailers, I'd say the Roman arms and armor are the best I've ever seen in a non-documentary film -- reenactor quality, almost. Except the spears, they suck.

As to the story itself, the fate of the Legio IX Hispana has been a subject of legend for years in Britain. The usual story is as depicted in this movie -- while marching through Scotland, they were ambushed and destroyed "Teutoberg Style". The actual historical record is a bit different; more recent research seems to indicate that the 9th Legion survived intact it's British service only to be redeployed to other parts of the Empire. Plus, there does not seem to be any literary sources for the supposed defeat (it seems the Romans were not adverse to discussing their losses -- most of our primary knowledge of such defeats as Carrhae, Teutoberg Wald, Arausio, and others comes from Roman sources). Perhaps the "defeat of the 9th Legion" legends are a sort-of revision of the real record, a victorious retelling of the battle of Mons Graupius. Who knows; anyway the story of a great Roman defeat at the hands of Britons/Picts/Druids/Ewoks/whatever remains and is stuck in folklore and legend, like plenty of other tall tales.