My persona is very early period, i.e. 600 BCE (and 5 minutes) — what would I wear?
“Welsh” isn’t really a meaningful term in 600 BCE, since that date is long before the divergence of the various Brythonic-speaking cultures (and quite possibly before the arrival of Brythonic-speaking culture in Britain at all!). So if you’re talking about “the cultural ancestors of the Welsh from 600 BCE” then you may, in fact, be talking about people on the continent participating in early La Tene culture (or late Hallstat culture). (Of course, culture and language are not the only “ancestors” of later Welsh culture — in all likelihood, the biological ancestors of the later Welsh included, at this date, a significant number of people living in the geographic region later to become Wales, but not yet speaking a Celtic language or participating substantially in what we know as “Celtic culture”. There is a major philosophical debate as to what the term “Celtic” really means, historically, which cannot entirely be avoided in this question.) About the only useful sources of information o