Description of druidic practices in Graves' Claudius the God - how factual are they?

How accurate are the details that Robert Graves gives of ancient British druidic practices in his novel Claudius the God? Did he draw from contemporary accounts (Caesar’s for example)? Or did he just make them all up?

I’m particularly intrigued by Graves’ description of the test of poetical composition given to candidates for the druidic priesthood:

I don’t know the answer, but beware of taking Graves at face value. There are some descriptions of Druidic practices in Caesar and (I think) other Roman writers, and Graves was well-read in the Roman works. But he also frequently made stuff up and passed it off as real, even in his non-fictional books. Perhaps I’m too harsh – Graves, I think, really did believe a lot of the things that he came up with about the past that had no actual documentary basis. He’s unapologetic about this in his works, and freely admits to it. He seemed to think he had a pipeline to the past. So read his fiction as entertainment, but if you plan on using his The Greek Myths or The White Goddess as resources, be sure to find a corroborating text.

I sincerely hope that in the future The White Goddess will be acclaimed as the great work of imaginative literature that it is.

FWIW, I’ve read that description of initiation someplace else, before – although IIRC it was for bardic initiation. Don’t remember where it’s from though. Maybe Frazier or Caesar.

Skull & Bones?

Thanks for the comments. I’ll assume that Graves’ description involves at least some embroidering of the facts.