there are medieval texts written by christian monks that document the migration of celtic speakers from spain to the british isles centuries before the romans arrived there and even further document the indo-european migration into spain itself, by documenting the original origin point of the celts as from scythia (ukraine). the celts of ireland and britain knew where they came from, but the christian monks vandalized and destroyed their indigenous history by filling it up with nonsense about adam and eve and noah's ark.

the modern dna evidence actually pretty convincingly demonstrates that the celts had a long concept of history and that the "pagan myths" kept as vandalized fairy tales by christian monks were actually startlingly accurate.

unfortunately, the romans thoroughly destroyed the celtic writing system (which we know now did in fact exist) during the celtic genocide, and they lost their history, their culture and their language and instead started speaking latin (to evolve into french, spanish and portugese) and then eventually germanic (in the form of english, dutch and dialects of german). only the welsh and irish (who migrated to scotland and separated into scottish in the historical period) survived. in later years, christians began disseminating the myth that there was no celtic history, and the celts never even developed writing, but the texts that were partially preserved by the christian monks, albeit in a vandalized state, clearly demonstrate the opposite.