Arthur's dog Cabal is the oldest named of all of Arthur's companions in legend, in fact. Dating from the 9th century "Wonders of Britain" compsed in Wales. It indeed comes from the Latin word for horse, presumably because it was a very big dog.
As the story makes clear, Arthur has been serving in the current Emperor's legions. He is not a hold-over from the Roman occupation of Britain.
As the story makes clear, Arthur has been serving in the current Emperor's legions. He is not a hold-over from the Roman occupation of Britain.