Thanks for reviewing Dolores and glad you're enjoying it.
I hope to be able to post chapters more often than once a month, but I'm going to be losing a lot of the time I use for writing, especially weekends.
Any parts of the story involving dragons or the Draig-Cyfrinachau are made up, however the rest is historically accurate (near enough).
For example, the Breton's did support William the Conqueror's invasion in 1066, but they also did support England during the early half of the Hundred Years War. The modern day Celtic languages (such as Welsh,Irish and Manx) are believed to have developed from a single language called proto-Celtic which experts are reconstructing (the other language mentioned, proto-Indo-European, is also believed to be a real language which is also being reconstructed) - although neither is thought to have been a written language. The Roman Empire's conquest of Angelsey (the last area in Wales to fall to the Romans) in 60 AD was delayed by the uprising of Boudica (Boadicea), who was from an area of England where they would have spoken a Celtic language called British - The Welsh were hiding British peoples on Angelsey, so these two were in theory allies. I have taken some poetic license in weaving these historical facts into the story, but there is nothing that is wildly inaccurate or made up.
I hope this answers your question. Though I'm glad people are getting so into the story.