Comment by cyocum

I have a degree in "Celtic Studies" and while I tend to study the Irish early medieval period rather than the ancient period, I would highly recommend reconsidering the entire idea of "Celtic". A couple of books that might be good to read if you have time are: John Collis, The Celts : origins, myths & inventions (https://www.worldcat.org/title/921219683) and Simon James, The Atlantic Celts : ancient people or modern invention? (https://www.worldcat.org/title/249450858). I have not had the time lately to read up on the state of the question so I will read the recommended article: Rachel Pope, Re-approaching Celts: Origins, Society, and Social Change (https://link.springer.com/article/10.1007/s10814-021-09157-1) with keen interest.