In Welsh mythology, Euroswydd is the father of Nisien and Efnysien by Penarddun, daughter of Beli Mawr. In the Second Branch of the Mabinogi Penarddun is the wife of Llyr, by whom her children are Bran, Branwen, and Manawydan. The circumstances of Nisien and Efnysien's conception are not described, but one of the Welsh Triads mentions that Eurosywdd had held Llyr captive as one of the Three Exalted Prisoners of Britain; it is likely the traditions are connected. Welsh mythology, the remnants of the mythology of the pre-Christian Britons, has come down to us in much altered form in medieval Welsh manuscripts such as the Red Book of Hergest, the White Book of Rhydderch, the Book of Aneirin and the Book of Taliesin. ... In Welsh mythology, Nisien was the son of Penarddun and Eurosswydd and twin of Efnisien. ... In Welsh mythology, Efnysien or Efnisien was the son of Penarddun and Euroswydd. ... In Welsh mythology, Penarddun was the wife of Llyr. ... Beli Mawr (Beli the Great) was a Welsh ancestor deity. ... The Four Branches of the Mabinogi are the best known tales from the medieval Welsh Mabinogion. ... The Mabinogion is a collection of prose stories from medieval Welsh manuscripts. ... In Celtic mythology, Lir (the sea) was the god of the sea, father of Manannan mac Lir, Bran, Branwen and Manawydan by Penarddun and a son of Danu and Beli. ... Bran the Blessed, also known as Bran Vendigaid, Bendigeidfran or Branovices, is a giant and king of Britain in Welsh mythology. ... In Welsh mythology, Branwen was a daughter of Llyr and Penarddun and has been interpreted as a goddess of love and beauty. ... In Welsh mythology, Manawydan, son of Llyr, is the equivalent of the Irish Manannan mac Lir and a presumed sea god. ... The Welsh Triads (Welsh, Trioedd Ynys Prydein) is used to describe any of the related Medieval collection of groupings of three that preserve a major portion of Welsh folklore and Welsh literature. ...

References

• Rachel Bromwich (editor and translator), Trioedd Ynys Prydein: The Welsh Triads, Cardiff: University of Wales Press, 1978. ISBN 0-7083-0690-X
• Jeffrey Gantz (translator), The Mabinogion, London and New York: Penguin Books, 1976. ISBN 0-14-044322-3
• Ifans, Dafydd & Rhiannon, Y Mabinogion (Gomer 1980) ISBN 1 85902 260 X