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 Celtic mythology and history were recorded orally by specialists such as druids (). This oral record has been lost or altered as a result of outside contact and invasion over the years. Much of this altered mythology and history is preserved in medieval Welsh manuscripts, which include the Red Book of Hergest, the White Book of Rhydderch, the Book of Aneirin and the Book of Taliesin. Other works connected to Welsh mythology include the ninth-century Latin historical compilation Historia Brittonum ("History of the Britons") and Geoffrey of Monmouth's twelfth-century Latin chronicle Historia Regum Britanniae ("History of the Kings of Britain"), as well as later folklore, such as the materials collected in The Welsh Fairy Book by William Jenkyn Thomas (1908). Legends The Four Branches of the Mabinogi Four of the mythological stories contained in the Mabinogion are collectively known as the Four Branches of the Mabinogi. They concentrate largely on the exploits of various British deities who have been Christianized into kings and heroes. The only character who appears in every branch is Pryderi fab Pwyll, the king of Dyfed, who is born in the first Branch, is killed in the fourth, and is probably a reflex of the Celtic god Maponos. The only other recurring characters are Pryderi's mother Rhiannon, associated with the peaceful British prince Manawydan, who later becomes her second husband. Manawyadan and his siblings Brân the Blessed ( or "Blessed Crow"), Branwen and Efnysien are the key players of the second branch, while the fourth branch concerns itself with the exploits of the family of Dôn, which includes the wizard Gwydion, his nephew, Lleu Llaw Gyffes, and his sister, Arianrhod. Pwyll, Prince of Dyfed The first branch tells of how Pwyll, prince of Dyfed, exchanges places for a year with Arawn, the ruler of Annwn (the otherworld), defeats Arawn's enemy Hafgan, and on his return encounters Rhiannon, a beautiful maiden whose horse cannot be caught up with. He manages to win her hand at the expense of Gwawl, to whom she is betrothed, and she bears him a son, but the child disappears soon after his birth. Rhiannon is accused of killing him and forced to carry guests on her