Arianrhod () is a figure in

Welsh mythology Welsh mythology (Welsh: ''Mytholeg Cymru'') consists of both folk traditions developed in Wales, and traditions developed by the Celtic Britons elsewhere before the end of the first millennium. As in most of the predominantly oral societies Celti ...

who plays her most important role in the

Fourth Branch In politics of the United States, the fourth branch of government is an unofficial term referring to groups or institutions perceived variously as influencing or acting in the stead of the three branches of the US federal government defined in the ...

of the ''

Mabinogi The ''Mabinogion'' () are the earliest Welsh prose stories, and belong to the Matter of Britain. The stories were compiled in Middle Welsh in the 12th–13th centuries from earlier oral traditions. There are two main source manuscripts, create ...

''. She is the daughter of

Dôn Dôn () is an ancestor figure in Welsh legend and literature. She is typically given as the mother of a group known as the "Children of Dôn", including Gwydion, Arianrhod, and Gilfaethwy, among many others. However, antiquarians of the early mod ...

and the sister of

Gwydion Gwydion fab Dôn () is a magician, hero and trickster of Welsh mythology, appearing most prominently in the Fourth Branch of the ''Mabinogi'', which focuses largely on his relationship with his young nephew, Lleu Llaw Gyffes. He also appears ...

and

Gilfaethwy In Welsh mythology, Gilfaethwy () was a son of the goddess Dôn and brother of Gwydion and Arianrhod in the Fourth Branch of the Mabinogi. His uncle Math fab Mathonwy, king of Gwynedd, must keep his feet in the lap of a young virgin at all time ...

; the

Welsh Triads The Welsh Triads ( cy, Trioedd Ynys Prydein, "Triads of the Island of Britain") are a group of related texts in medieval manuscripts which preserve fragments of Welsh folklore, mythology and traditional history in groups of three. The triad is a ...

give her father as

Beli Mawr Beli Mawr ("Beli the Great") was an ancestor figure in Middle Welsh literature and genealogies. He is the father of Cassivellaunus, Arianrhod, Lludd Llaw Eraint, Llefelys, and Afallach. In certain medieval genealogies he is listed as the son or h ...

.Triad 35. Bromwich, ''Trioedd Ynys Prydein'', pp. 284–285. In the ''Mabinogi'' her uncle

Math ap Mathonwy In Welsh mythology, Math fab Mathonwy (), also called Math ap Mathonwy (Math, son of Mathonwy) was a king of Gwynedd who needed to rest his feet in the lap of a virgin unless he was at war, or he would die. The story of Math is the fourth of the ...

is the King of Gwynedd, and during the course of the story she gives birth to two sons,

Dylan ail Don Dylan ail Don () (in Middle Welsh) is a character in the Welsh mythic Mabinogion tales, particularly in the fourth tale, "'' Math fab Mathonwy''". The story of Dylan reflects ancient Celtic myths that were handed down orally for some generations b ...

and

Lleu Llaw Gyffes Lleu Llaw Gyffes (, sometimes spelled Llew Llaw Gyffes) is a hero of Welsh mythology. He appears most prominently in the Fourth Branch of the Mabinogi, the tale of Math fab Mathonwy, which tells the tale of his birth, his marriage, his death, his ...

, through magical means.

Mabinogion

According to the Fourth Branch (circa 12th century), Arianrhod's uncle

Math fab Mathonwy In Welsh mythology, Math fab Mathonwy (), also called Math ap Mathonwy (Math, son of Mathonwy) was a king of Gwynedd who needed to rest his feet in the lap of a virgin unless he was at war, or he would die. The story of Math is the fourth of the ...

would die if he didn't keep his feet in the lap of a virgin when he was not at war. Gilfaethwy conceives a lust for Math's original footholder, pretty Goewin, and he and his brother

engineer a war with King Pryderi of Kingdom of Dyfed, forcing Math to leave his court. In Math's absence Gilfaethwy rapes Goewin. When Math returns he punishes his nephews severely by turning them into a series of mated pairs of animals, and marries Goewin to alleviate her shame. However, he must find a new virgin to hold his feet. Gwydion suggests his sister, Arianrhod. To test her virginity, Math tells her to step over his magician's rod. On doing this, however, she immediately gives birth to a young boy,

, and a blob-like entity which becomes

. Dylan is a sea spirit, who flees to the ocean immediately after he is baptized. Gwydion grabs Lleu Llaw Gyffes before anyone else sees it and places it in a chest. Before long it becomes a boy who grows at twice the normal rate; when he is four he is as big as an eight-year-old. Gwydion takes him to see his mother at her home,

Caer Caer (; owl, cair or ') is a placename element in Welsh meaning "stronghold", "fortress", or "citadel", roughly equivalent to an Old English suffix (''-ceaster'') now variously written as , , and .Allen, Grant.