The arrival of the Celtic race to the "ends of the world" would of course lead to the British isles. This is the foundation of the language, culture, society, and lore of the peoples that were to become Welsh. Of course there were the Irish, Scots, Cornish, Isle of Man, and the Britons who shared these roots. Celtic Britain written by Lloyd Laing is such a book.
1) Introduction - the Celts in Europe
2) Iron Age Britain
3)The Roman Interlude
4)The Dark Ages
5)Epilogue - Celtic Twilight
There are 109 plates (mostly pictures) contained within the pages. [I like pictures!] It was published 1979, by Charles Scribner's Sons, New York. A fun kind of book.