Although many of the manuscripts containing texts relating to Irish mythology have failed to survive, and much more material was probably never committed to writing, there is enough remaining to enable the identification of four distinct, if overlapping, cycles: the Mythological Cycle, The Ulster Cycle, the Fenian Cycle and the Historical Cycle. There are also a number of extant mythological texts that do not fit into any of the cycles. In addition, there are a large number of recorded folk tales that, while not strictly mythological, feature personages from one or more of these four 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 The 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 and some can, on linguistic grounds, be dated back as far as the 5th or 6th centuries. Other important sources include a group of four manuscripts originating in the west to Ireland in the late 14th or early 15th centuries: 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 the earliest know version of the Táin Bó Cúailnge 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) (c. 1640), particularly as these later compilers and writers my 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. 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.
The Mythological Cycle
The Mythological Cycle 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 Etain and the stories of the first and second battles of Mag Tuireadh. One of the greatest of all Irish stories, Oidheadh Clainne Lir, or The Tragedy of the Children of Lir, is also part of this cycle.
Lebor Gabala Erren is a pseudo-history of Ireland, tracing the ancestry of the Irish back to Noah. It is concerned with the people known as the Tuatha de Danaan, who were believed to have inhabited the island before the arrival of the Celts. They faced opposition from their enemies, the Fomorians, led by Balor of the Evil Eye. Balor was eventually slain by Lugh Lamfada (Lug of the Long Arm) at the second battle of Mag Tuireadh. With the arrival of the Celts, the Tuatha de Danaan 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 de Danaan were defeat by the Milesians, or Celtic Irish.
It is important to note that the Tuatha de Danaan were not viewed so much as gods as the shape-shifting magician population of an earlier Golden Age Ireland. Although the Irish revered the fairy folk, there is little evidence to support the assertion that, with the possible exception of the pan-Celtic figure of Lugh, they ever actually worshiped them as gods.
Other important Tuatha de Danaan figures
The Ulster Cycle
The Ulster Cycle is set around the beginning of the Christian era and most of the action takes place in the provinces of Ulster and Connaught. It consists of a group of heroic stories dealing with the lives of Conchobar Mac Neassa, king of Ulster, the great hero Cu Chulainn, the son of Lugh, and of their friends, lovers, and enemies. These are the Ulaid, or people of the North-Western corner of Ireland and the action of the stories centres round the royal court at Emain Macha, close to the modern city of Armagh. The Ulaid had close links with the Irish colony in Scotland, and part of Cu Chulainn's training takes place in that colony.
The cycle consists of stories of the births, early lives and training, wooings, battles, feastings and deaths of the heroes and reflects a warrior society in which warfare consists mainly of single combats and wealth is measured mainly in cattle. These stories are written mainly in prose. The centrepiece of the Ulster Cycle is the Táin Bó Cúailnge. Other important Ulster Cycle tales include The Exile of the Sons of Usnech, The Tragic Death of Aife's only Son, The Story of Bricriu's Feast, and The Destruction of Ua Derga's Hostel. The great tale of Deirdre of the Sorrows, source for John Millington Synge's play of the same name, is also associated with this cycle.
This cycle is, in some respects, close to the mythological cycle. Some of the characters from the latter reappear, and the same sort of shape-shifting magic is much in evidence. Again it is evident that the characters of Irish mythology are not so much gods as heroes possessed of superhuman powers. Elements of the Ulster Cycle, such as Cu Chulainn's magic spear and the motif of the Champion's Ordeal in The Story of Bricriu's Feast, have been shown to be the sources of parts of the Matter of Britain.
The Fenian Cycle
Like the Ulster Cycle, the Fenian Cycle is concerned with the deeds of Irish heroes. The stories of the Fenian Cycle appear to be set around the 3rd century and mainly in the provinces of Leinster and Munster. They differ from the other cycles in their strength of their links with the Irish-speaking community in Scotland and there are many extant Fenian texts from that country. They also differ from the Ulster Cycle in that the stories are told mainly in verse and that in tone they are nearer to the tradition of romance than the tradition of epic. The stories concern the doings of Fionn mac Cumhail and his band of soldiers, the Fianna.
The single most important source for the Fenian Cycle is the Acallamh na Senórach (Colloquy of the Old Men)), which is found in two 15th century manuscripts, the Book of Lismore and Laud 610 as well as a 17th century manuscript from Killiney, Co Dublin. The text is dated from linguistic evidence to the 12th century. The text records conversations between the last surviving members of the Fianna and St Patrick and runs to some 8,000 lines. The late dates of the manuscripts may reflect a longer oral tradition for the Fenian stories.
The Fianna of the story are divided into the Clann Baiscne, led by Fionn, and the Clann Morna, led by his enemy, Goll mac Morna. Goll killed Fionn's father, Cumall in battle and the boy Fionn is brought up in secrecy. As a youth, he is being trained in the art of poetry, when he accidentally eats part of the Salmon of Knowledge, which makes him wise in all things. He takes his place as the leader of his band and numerous tales are told of their adventures. Two of the greatest Irish tales, Toraigheacht Dhiarmada agus Ghrainne (The Pursuit of Diarmaid and Grainne) and Oisin in Tir na nOg form part of the cycle. The Diarmaid and Grainne story, which is one of the few Fenian prose tales, is the Celtic source of Tristan and Isolde.
The world of the Fenian Cycle is one in which professional warriors spend their time hunting, fighting, and engaging in adventures in the spirit world. New entrants into the band are expected to be knowledgeable in poetry as well as undergo a number of physical tests or ordeals. Fionn is a kind of Irish King Arthur, leading his band of warriors wisely in an endless battle against evil. Again, there is no religious element in these tales unless it is one of hero-worship.
It was part of the duty of the medieval Irish bards, or court poets, to record the history of the family and the genealogy of the king they served. This they did in poems that blended the mythological and the historical to a greater or lesser degree. The resulting stories form what has come to be known as the Historical Cycle, or more correctly Cycles, as there are a number of independent groupings.
The kings that are covered range from the almost entirely mythological Labraid Loinsech, who became High King of Ireland around 431 BCE to the entirely historical Brian Boru. However, the greatest glory of the Historical Cycle is the Buile Shuibhne (The Frenzy of Suibhne), a 12th century told in verse and prose.
Suibhne, king of Dal nAride, was cursed by St Ronan and became a kind of half man, half bird, condemned to live out his life in the woods, fleeing from his human companions. The story has captured the imaginations of contemporary Irish poets and has been translated by Trevor Joyce and Seamus Heaney.
The adventures, or echtrae, are a group of stories of visits to the Irish Other World. The most famous, Oisin in Tir na nOg belongs to the Fenian Cycle, but several free-standing adventures survive, including The Adventure of Conle, The Adventure of Bran mac Ferbail and The Adventure of Laegaire.
The voyages, or immrama, are tales of sea journeys and the wonders seen on them. These probably grew from the experiences of fishermen combined with the Other World elements that inform the adventures. Of the seven immrama mentioned in the manuscripts, only three survive: The Voyage of Mael Duin, The Voyage of the Ui Chorra, and The Voyage of Snedgus and Mac Riagla. The Voyage of Mael Duin is the forerunner of the later Voyage of St Brendan.
At the beginning of the 19th Century, Herminie T. Kavanagh wrote down many Irish folk tales which she published in magazines and in two books. Twenty-six years after her death, the tales from her two books, Darby O'Gill and the Good People, and Ashes of Old Wishes were made in to the film Darby O'Gill and the Little People.
Primary Sources in English Translation
Primary sources in Medieval Irish
Retellings of the myths in English