Shape-shifting quite after the fairy fashion is very frequently met with in old Celtic literature. Thus, in the Rennes _Dinnshenchas_ there is this passage showing that spirits or fairies were regarded as necessary for the employment of magic:--'Folks were envious of them (Faifne the poet and his sister Aige): so they loosed elves at them who transformed Aige into a fawn' (the form assumed by the fairy mother of Oisin, see p. 299 n.), 'and sent her on a circuit all round Ireland, and the fians of Meilge son of Cobthach, king of Ireland, killed her.'[179] A fact which ought to be noted in this connexion is that kings or great heroes, rather than ordinary men and women, are very commonly described as being able to shift their own shape, or that of other people; e. g. 'Mongan took on himself the shape of Tibraide, and gave Mac an Daimh the shape of the cleric, with a large tonsure on his head.'[180] And when this fact is coupled with another, namely the ancient belief that such kings and great heroes were incarnations and reincarnations of the Tuatha De Danann, who form the supreme fairy hierarchy, we realize that, having such an origin, they were simply exercising in human bodies powers which their divine race exercise over men from the fairy world (see our chapter iv). In Brythonic literature and mythology, magic and witchcraft with the same animistic character play as great or even a greater rôle than in Gaelic literature and mythology. This is especially true with respect to the Arthurian Legend, and to the _Mabinogion_, some of which tales are regarded by scholars as versions of Irish ones. Sir John Rhŷs and Professor J. Loth, who have been the chief translators of the _Mabinogion_, consider their chief literary machinery to be magic (see our chapter v). So far it ought to be clear that Celtic magic contains much animism in its composition, and that these few illustrations of it, selected from numerous illustrations in the ancient Fairy-Faith, confirm Pliny's independent testimony that in his age the Britons seemed capable of instructing even the Persians themselves in the magical arts. _European and American Witchcraft_