Possible
capital of Rheged found at Trusty's (i.e. Tristan/Drustan's) Hill. I'm sorry the writers have referred to the French romance/Malory tradition and not to
Taliesin.
I also want to swat the morons in the comments making an England/Scotland thing out of this: Rheged extends from Galloway into Cumbria and was a Brythonic kingdom. However, it just intensifies my anger at the Scottish government's Gaelicisation of place-names at stations: imposing bilingual signage that eradicates the real history and culture of Brythonic, Anglian and Norse settlements. It's phoney Highlandism on a par with the Victorians following Scott and wrapping everything in tartan.