The myth of Rhiannon is recalled in the first and third Branches of the Mabinogi, although her presence is also felt at the end of the Second Branch. Aside from her son Pryderi, and the latter’s avatar Lleu in the Mabinogi of Math, it can be seen that Rhiannon is without doubt one of the most significant personages in the Four Branches as a whole. She plays a leading part in the First and Third Branches, and her presence can be felt to varying degrees elsewhere in the Mabinogi as well.
The name Rhiannon, literally means ‘Great Queen’. It seems likely that this name was one of a number of epithets for the Great Goddess (whose more personal names would have been a closely guarded mystery). She played a number of roles familiar to Celtic mythology: the Otherworld Mistress, the Calumniated Wife and finally the Sovereign Queen. Earlier prototypes of this Rhiannon, whose mythology is expounded in First and Third branches, can be found in the pagan goddesses Matrona ‘Great Mother’, and Epona, the Gaulish horse goddess found throughout Europe, as far apart as Rome and Hadrien’s Wall. The myth of Rhiannon represents the transitional point from the pagan rituals of the Horse Goddess cult, into its sublimated form: the chivalric mysteries of courtly love.
Within the Mabinogi, Rhiannon has particularly close links with Dyfed. As befits the Sovereignty Goddess, she has as her consort the king of this territory: first in the person of Pwyll, and secondly in Manawydan son of Llŷr. Her origins most likely belong in this region of Southwest Wales, where a localised version of the Goddess cult appears to have integrated the various diverse elements which made up her myth in medieval times.
Outside the Mabinogi, Rhiannon is less well known - compounding the suggestion that she was, after all, an essentially local figure. The only other reference in the ancient books of Wales occurs in the primitive Arthurian tale of ‘Culhwch and Olwen’, in which the chthonic giant Ysbaddaden requests ‘the birds of Rhiannon’ for his daughter’s wedding day (which will also be the last day of his on life) whose singing could ‘wake the dead, and ease the living to sleep’. These same birds make an appearance in the Mabinogi of Branwen, soon after the Children of Llŷr are sojourning in the Island Otherworld.
Rhiannon’s associations with horses, magical birds and the Island Otherworld place her in a well-established tradition within the Celtic world, as does her mysterious origins, and her unjust treatment at the hands of her host community. She also exemplifies the medieval author’s artistry at its very best: wherein mythic archetypes are also represented in the human dimension: with distinct emotional and social characteristics which can touch us even today. Through the figure of Rhiannon, a powerful presence is evoked: we come to know and respect this unique personality through her the power of her words and wisdom of forbearance. But like any three-dimensional character she is not without her occasional flaws: some of her less thoughtful actions carry serious repercussions . However, so carefully does the author create this synthesis of the deeply human with the divine, that her endurance of the tragic yet redemptive fate as the Horse Goddess carries an unusually powerful psycho-dramatic affect.
The nature of the proto-historic cult of *Rigantona has been considered in the appendix of my study of the Four Branches of the Mabinogi (2005).