Welsh mythology 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 and Geoffrey of Monmouth's twelfth-century Latin chronicle Historia Regum Britanniae, as well as later folklore, such as the materials collected in The Welsh Fairy Book by William Jenkyn Thomas (1908).
The Two Kings (sculptor Ivor Roberts-Jones, 1984) near Harlech Castle, Wales. Brân the Blessed carries the body of his nephew Gwern.
The opening lines of Lludd and Llefelys (Bodleian Library's manuscript)
History of the Kings (f.75.v) King Arthur
The opening lines of Culhwch and Olwen, from the Red Book of Hergest
Celtic mythology is the body of myths belonging to the Celtic peoples. Like other Iron Age Europeans, Celtic peoples followed a polytheistic religion, having many gods and goddesses. The mythologies of continental Celtic peoples, such as the Gauls and Celtiberians, did not survive their conquest by the Roman Empire, the loss of their Celtic languages and their subsequent conversion to Christianity. Only remnants are found in Greco-Roman sources and archaeology. Most surviving Celtic mythology belongs to the Insular Celtic peoples. They preserved some of their myths in oral lore, which were eventually written down by Christian scribes in the Middle Ages. Irish mythology has the largest written body of myths, followed by Welsh mythology.
The Celtic god Sucellus
Votive Celtic wheels thought to correspond to the cult of Taranis. Thousands of such wheels have been found in sanctuaries in Gallia Belgica, dating from 50 BCE to 50 CE. National Archaeological Museum, France
Riders of the Sidhe, a 1911 painting of the aos sí or Tuatha Dé Danann, by the artist John Duncan
An illustration of Llŷr and the swans by H. R. Millar