It was chiefly during the twelfth and thirteenth centuries that the Arthurian Legend as a thing of literature began to take definite shape. The old romances of the Brythons were cultivated and revised, and written down by men and women of literary genius. Chrétien de Troyes, who recorded a large number of legendary stories in verse, Marie de France, famous for her _Lais_, Thomas, the author of the chief version of the _Tristan_ legend,[304] Béroul, who recorded a less important version of this legend,[305] and Robert de Boron, who did much to develop the legend of the Holy Grail, were among the greatest workers in the French Celtic Revival of this time. Professor Brown has shown that 'almost every incident in Chrétien's _Iwain_ was suggested by an ancient Celtic tale, dealing with the familiar theme of a journey to win a fairy mistress in the Otherworld.'[306] The fay whom Iwain marries is called Laudine; and, like one of the fairies who live in sacred waters, she has her favourite fountain which the knight guards, as though he were the Black Knight in the old Welsh tale of _The Lady of the Fountain_. Both Gaston Paris and Alfred Nutt have also recognized the tale of _Iwain_ as a fairy romance.[307] Professor Loth observes that, 'It is not impossible that Chrétien had known, among fairy legends, Armorican legends, concerning the fairies of waters, whose rôle is identical with that of the Welsh _Tylwyth Teg_.'[308] In _Lanval_, one of the _Lais_[309] by Marie de France, written during the twelfth century, probably while its author was living in England, we have direct proof that there was then flourishing in Brittany--well known to Marie de France, who was French by birth and training--a popular belief in fairy women who lived in the Otherworld, and who could _take_ mortals on whom their love fell. It is probable that the older lay, to which Marie de France refers in the beginning of her _Lanval_, may have been the anonymous one of _Graelent_, sometimes improperly attributed to her. Zimmer and Foerster place the origin of _Graelent_ in Brittany[310]; and the similarity of the heroes in the two poems seems to be due to a very ancient Brythonic Fairy-Faith. Dr. Schofield sees in _Graelent_ an older form of the more polished _Lanval_; and remarks that the chief difference in the two _lais_ is found in the way the hero meets the fairy women. In the case of Lanval, when he leaves the court, he goes to rest beside a river where two beautiful maidens come to him; Graelent is alone in the woods when he sees a hind whiter than snow, and following it comes to a place where fairy damsels are bathing in a fountain. There seems to be no doubt that in both poems the maidens and damsels are fairies quite like the Tuatha De Danann, with power to cast their spell over beautiful young men whom they wish to have for husbands. In _Guingemor_, another of the old Breton lays, ascribed by Gaston Paris to Marie de France, we find again fairy-romance episodes