The mythology of pre-Christian Ireland did not entirely survive the conversion to Christianity, but much of it was preserved, shorn of its religious meanings, in medieval Irish literature, which represents the most extensive and best preserved of all the branch and the Historical Cycle. There are also a number of extant mythological texts that do not fit into any of the cycles. Additionally, there are a small number of recorded folk tales that, while not strictly mythological, feature personages from one or more of these nine cycles.
The three main manuscript sources for Irish mythology are the late 11th/early 12th century Lebor na hUidre which is in the library of the Royal Irish Academy, the early 12th century Book of Leinster in the Library of Trinity College, Dublin, and the Rawlinson manuscript B 502 (Rawl.), housed in the Bodleian Library at Oxford University. Despite the dates of these sources, most of the material they contain predates their composition. The earliest of the prose can be dated on linguistic grounds to the 9th century, and some of the verse may be as old as the 6th century. Other important sources include a group of four manuscripts originating in the west of Ireland in the late 14th or early 15th century: The Yellow Book of Lecan, The Great Book of Lecan, The Book of Hy Many, and The Book of Ballymote. The first of these contains part of the earliest known version of the Táin Bó Cúailnge ("The Driving-off of Cattle of Cooley") and is housed in Trinity College. The other three are in the Royal Academy. Other 15th century manuscripts, such as The Book of Fermoy also contain interesting materials, as do such later syncretic works such as Geoffrey Keating's Foras Feasa ar Éirinn (The History of Ireland) (ca. 1640), particularly as these later compilers and writers may have had access to manuscript sources that have since disappeared. When using these sources, it is, as always, important to question the impact of the circumstances in which they were produced. Most of the manuscripts were created by Christian monks, who may well have been torn between the desire to record their native culture and their religious hostility to pagan beliefs resulting in some of the gods being euhemerized. Many of the later sources may also have formed part of a propaganda effort designed to create a history for the people of Ireland that could bear comparison with the mythological descent of their British invaders from the founders of Rome that was promulgated by Geoffrey of Monmouth and others. There was also a tendency to rework Irish genealogies to fit into the known schema of Greek or Biblical genealogy. It was once unquestioned that medieval Irish literature preserved truly ancient traditions in a form virtually unchanged through centuries of oral tradition back to the ancient Celts of Europe. Kenneth Jackson famously described the Ulster Cycle as a "window on the Iron Age", and Garret Olmsted has attempted to draw parallels between Táin Bó Cuailnge, the Ulster Cycle epic, and the iconography of the Gundestrup Cauldron. However, this "nativist" position has been challenged by "revisionist" scholars who believe that much of it was created in Christian times in deliberate imitation of the epics of classical literature that came with Latin learning. The revisionists would indicate passages apparently influenced by the Iliad in Táin Bó Cuailnge, and the existence of Togail Troí, an Irish adaptation of Dares Phrygius' De excidio Troiae historia, found in the Book of Leinster, and note that the material culture of the stories Mythological cycle
The Mythological Cycle, comprising stories of the former gods and origins of the Irish, is the least well preserved of the four cycles. The most important sources are the Metrical Dindshenchas or Lore of Places and the Lebor Gabála Érenn or Book of Invasions. Other manuscripts preserve such mythological tales as The Dream of Aengus, The Wooing Of Étain and Cath Maige Tuireadh, The (second) Battle of Magh Tuireadh. One of the best known of all Irish stories, Oidheadh Clainne Lir, or The Tragedy of the Children of Lir, is also part of this cycle. Lebor Gabála Érenn is a pseudo-history of Ireland, tracing the ancestry of the Irish back to Noah. It tells of a series of invasions or "takings" of Ireland by a succession of peoples, the fifth of whom was the people known as the Tuatha Dé Danann ("Peoples of Goddess Danu"), who were believed to have inhabited the island before the arrival of the Gaels, or Milesians. They faced opposition from their enemies, the Fomorians, led by Balor of the Evil Eye. Balor was eventually slain by Lug Lámfada (Lug of the Long Arm) at the second battle of Magh Tuireadh. With the arrival of the Gaels, the Tuatha Dé Danann retired underground to become the fairy people of later myth and legend. The Metrical Dindshenchas is the great onomastic work of early Ireland, giving the naming legends of significant places in a sequence of poems. It includes a lot of important information on Mythological Cycle figures and stories, including the Battle of Tailtiu, in which the Tuatha Dé Danann were defeated by the Milesians. It is important to note that by the Middle Ages the Tuatha Dé Danann were not viewed so much as gods as the shape-shifting magician population of an earlier Golden Age Ireland. Texts such as Lebor Gabála Érenn and Cath Maige Tuireadh present them as kings and heroes of the distant past, complete with death-tales. However there is considerable evidence, both in the texts and from the wider Celtic world, that they were once considered deities. Even after they are displaced as the rulers of Ireland, characters such as Lug, the Mórrígan, Aengus and Manannan appear in stories set centuries later, betraying their immortality. A poem in the Book of Leinster lists many of the Tuatha Dé, but ends "Although [the author] enumerates them, he does not worship them". Goibniu, Creidhne and Luchta are referred to as Trí Dé Dána ("three gods of craftsmanship"), and the Dagda's name is interpreted in medieval texts as "the good god". Nuada is cognate with the British god Nodens; Lug is a reflex of the pan-Celtic deity Lugus, the name of whom may indicate "Light"; Tuireann may be related to the Gaulish Taranis; Ogma to Ogmios; the Badb to Catubodua.is generally closer to the time of the stories' composition than to the distant past. A consensus has emerged which encourages the critical reading of the material.
Other important Tuatha Dé Danann figures
- Dian Cecht
- Aes Sídhe
- Bean Sídhe