What are some good sources about the kingdom of dumnonia and the spread of Christianity in about the 4th century adI want to write a story set during that time but I can't find tons of information about, and even less about the druidic practices which were lost as Christianity metastasized throughout the British isles
Short of the sources under the wiki for "Dumnonia", I can't give much more historical, but I can give you a fictional for 'tone'. Try looking for Bernard Cornwell's "Warlord Chronicles". It's his take on a 'realistic' King Arthur, and while it could be brushed off (somewhat unfairly) as "Sharpe with shieldwalls", it does have some nice interactions and explorations of beliefs and cultures, the old religion in the face of the new. Plus there might be further reading/bibliographies as appendices; I've lost my copies so I can't check, but I think he's done it before.
>>18541781>the druidic practicesYou might want to look up Blood and Mistletoe: The History of the Druids in Britain by Ronald Hutton. It's super exhaustive, but the conclusions are grim: we know barely anything about druids, and people have mostly been making shit up about them for centuries.
>>18542624that's what I was afraid of considering it was an oral tradition. I'm sure some of the practices survived as Christian rites, but I don't know enough about Christianity to have a feel for what might be cloaked druidism
>>18541781tangentially related but are there any detailed writings about the religious beliefs of st. kilda islanders? some 18th century authors thought they were the last druids. they really weren't, but since they didn't have a catholic priest to serve the island for hundreds of years a sort of animistic folk religion filled the void (despite its practitioners remaining ostensibly christian)