My modules (and soon-to-be published novels) all take place in the Britain following Rome's departure and collapse, and the oncoming invasions of the Saxons from Germany, the 5th and 6th centuries. This was a short-lived golden age in which the native Celts were reclaiming their lands after the four hundred years of Roman occupation, it is also the era of my academic specialty and studies. Britain was a completely different place then.
There was no England, Wales, Cornwall and Scotland. It was a hodgepodge of kingdoms and tribes that all spoke roughly Welsh or Cornish, or the early stages of it. For a better word they spoke Neo-Brittonic or Old Brythonic, a language that will gradually evolve into Welsh, Cornish, Breton and Cumbrian in time as their populations become disjointed and forced to move west by the advance of Saxons, Frisians, Angles and Jutes.
This was the 'Age' of Arthur and other numerous warlords that fought and opposed the invasions from all sides, and it is one that I identify with strongly for reason unknown. The shift in language occurred going from a Synthetic one (Latin for example) to an Inflective form (modern European languages) and culturally much was carried with it from the old world when the Celts once populated nearly ALL of Europe. It was also a period in which the ancient people reinvented themselves too, they had to, or they would perish like the Celts of the Continent (Gauls, Galatians and the rest).
Sadly the majority of the places, kingdoms and locations (from a native Celtic perspective) have been lost in time, swept aside by the Germanic invaders and their language (the one you are reading). My Welsh and Cornish isn't as good as it should be, but then again I am in a part of the country where 'Celtic' is assumed to be either Irish or Scottish only and no one speaks any of them. So I have little chance to communicate in these wonderful languages.
If I am anything, I am a gwlatgar (patriot) for the Britons, the native Celts of Britain, and have a genetic link to them through my dad's side. I have been drawn to my ancestry, in this strain, for as long as I have been into gaming. When I return to university to earn my PhD in Celtic Studies it will be to further more in Brythonic studies in some way. But until then, my gaming books will suffice and give small glimpses of that world through a magical lens...