Such fairy romances as the above (and they are but a few examples selected from among a vast number) often localized in Brittany, raise the perplexing and far-reaching problem concerning the origin of the 'Matter of Britain'. The most reasonable position to take with respect to this problem would seem to be that Celtic traditions flourished wherever there were Gaels and Brythons, that there was much interchange of these traditions between one Celtic country and another--especially between Wales and Ireland and across the channel between Brittany and South England, including Cornwall and Wales, both before and after the Christian era. Further, the Arthurian fairy-romances, based upon such interchanged Celtic traditions, grew up with a Brythonic background, chiefly after the Norman Conquest, both in Armorica and in Britain, and became in the later Middle Ages one of the chief glories of English and of European literature. In concluding this slight examination of Brythonic fairy-romances, we may very briefly suggest by means of a few selected examples what fairies are like in the _Mabinogion_ stories and in the _Four Ancient Books of Wales_. _Kulhwch and Olwen_, the chief literary treasure-house of ancient magical and mystical Otherworld and fairy traditions of the Brythons, which we have already considered in relation to Arthur, 'appears to be built upon Arthurian and other legends of native growth.'[316] Unmistakable Welsh parallels to the Irish fairy-belief appear in the _Mabinogi of Pwyll, Prince of Dyfed_, where the two chief incidents are Pwyll's journey to the Otherworld after he and Arawn its ruler have exchanged shapes and kingdoms for a year, and the marriage of Pwyll to a fairy damsel; in the _Mabinogi_ of _Manawyddan_, which contains much magic and shape-shifting, and the description of a fairy castle belonging to Llwyd; and in the _Mabinogi_ of _Branwen, the Daughter of Llyr_, where there is the episode of the seven-year feast at Harlech over the Head of Bran, during which the Birds of Rhiannon's realm sing so sweetly that time passes abnormally fast. The subject-matter of the four true _Mabinogion_ (composed before the eleventh century) is, as Sir John Rhŷs has pointed out, the fortunes of three clans of superhuman beings comparable to the Irish Tuatha De Danann: (1) the Children of Llyr, (2) the Children of Don, (3) and the Family of Pwyll.[317] Herein, then, the ancient Gaelic and Brythonic Fairy-Faiths coincide, and show the unity of the Celtic race which evolved them.