Celtic mythology was not documented until the monks in the early Middle Ages (circa 8th century) gathered the mythology of the Celts, particularly the Irish. They recorded the Celtic oral traditions of the people and may have had access to stories recorded in Ogham by the later druids. Their goal was to construct a history of the Celts but, in the process, they rewrote the “pagan” stories with a Christian twist, in particular, turning the old gods into mortals which confused the stories.
The best record of the Celtic mythological tradition is contained in four cycles recorded by 12th century by Christian scribes: the Mythological Cycle, the Ulster Cycle, the Fenian (Fianna) Cycle, and the Kings (Historical) Cycle. The Mythological Cycle refers to the stories in Irish literature which describe the activities of otherworld characters with the successive invasions of Ireland by supernatural clans. The invasions are described in the Lebor Gabála (Book of Invasions). The last invaders were the Milesians who were the fictional first human ancestors of the Irish people who defeated the Tuatha Dé Danann.
The Fenian Cycle describes the Fenians (Fianna) who were a legendary band of heroes who defended Ireland and Scotland and kept law and order and hunted, a lot. The tales of the Fianna are heroic and fantastic, incorporating a lot of interaction with the gods. Their leader was the mythical Fionn mac Cumhaill.
The Ultonian Cycle includes a large body of heroic tales describing the activities of the Ulaidh, an ancient people from the whom the province of Ulster got its name. Cúchulainn, reputed to be son of the sun god Lugh, was Ulster’s greatest hero. He was trained in arms by the female warrior Scathach. The King’s (Historical) Cycle is a book of tales chronicling historical or semi-historical kings of Ireland, from the earliest times in the first century AD to the Middle Ages.
Tomorrow, More on Celtic Mythology Rita Bay