Little is known in detail of pre-Christian sanctuaries in Ireland, although ritual centres undoubtedly existed. Owing to the conservation of oral tradition in Ireland, however, a rich corpus of mythology survived to be written down in the early Christian period. The remarkable affection of the Celts in Ireland for their pre-Christian past allowed them, without compromising their newly won faith, to preserve something of their pagan tradition. Some of the individuals who figure in the myths were undoubtedly gods, although Christian ethics did not permit them to be represented as such. It is possible to establish correlations between certain details relating to places and things, and even aspects of behaviour, as recounted in the literature, and archaeological material, particularly that of the continental and insular Celts of the La Tène period [in modern Switzerland]. A close study of these correlations and their interpretation is difficult and, if uncritical, may be misleading. Much remains to be done, but such a study is essential in any attempt to understand the beliefs of the pre-Christian Celts.
Turning to the literature itself, there are, for example, traces of the triad of Gaulish divinities in three goddesses concerned with battle and death who occur in Irish stories, although here the goddesses do not occur as a triad, but individually. These are the Mórrígan, ‘the great Queen, and Macha and Badb. Badb is the essential goddess of battle, and frequently appears as a crow or a raven. The Mórrígan is thought to be the forerunner of Morgan la Faye in the medieval Arthurian Cycle. But she was  an unpleasant person. An ancient elegy tells ofa Leinster prince who was drowned in his little curagh, and of the ‘hateful laugh of the woman (the Mórrígan) who ‘has flung her white mane [the breakers] against Coning in his curagh. Of Macha we hear comparatively little. Brigantia also is attested by inscriptions in both Gaul and Britain. According to Cormacs Glossary she is the daughter of the Dagdá and the patron of poets, but she forms a triad with her two sisters who are the goddesses of smiths and laws, an odd association. She is believed to have been Christianized as St Brigid.
With the pious intention of elucidating the history of the earlier population of Ireland, the learned Irish of early Christian times schematized the arrival of the earlier inhabitants and their gods into a series of invasions, the latest provided with biblical respectability. A similar concept is found in early Welsh literature, and was drawn on by Nennius, so it must be at least as old as the early ninth century. A comparable tradition continued in Irish literature until well into the later medieval period. In Ireland the tradition is formalized under the heading Lebor Gabála (The Book of Invasions). First comes an invasion from Spain led by Parthalón, all of whose members perished of a plague. The second invasion was led by Nemed mac Agnomain, who after some years returned to Spain, being hard pressed by other invaders, the Formori; but eventually they returned to Ireland and colonized it. Later came the Fir Bolg, a race of agriculturalists from Greece, together with the Fir Gálioin and FirDomnann. These names respectively are cognate with the Belgae, the Gauls and the Damnonii (or Dumnonii), and may refer to the arrival of specific tribal groups. Then came the Tuatha Dé Danann, ‘the tribes of the goddess Danu, led by their poet Amargin, who landed on Irish sod and conquered first the Fir Bolg and later the Formori in two battles fought at Moytura. In the second Battle of Moytura the Formori were finally banished overseas, leaving the Tuatha Dé Danann in  possession. In this last battle Lugh came from overseas to lead them, for he possessed ‘all the arts and so was accepted as the leader.
The last to arrive were the Milesians, the sons of Míl. This was a late, and probably spurious tradition, presumably intended to confer Christian respectability on the immediate forebears of the Celts in Ireland. For the Tuatha Dé Danann were the gods of the Celts, and the purpose underlying the introduction of the Milesians was to allow them to displace the by then embarrassing Tuatha and to cover up the implications of their pre-Christian ritual and beliefs. The Lebor Gabála presumably the official version, has it that the Tuatha were banished from Ireland, but other widespread and perhaps more popular traditions, sympathetic to and nostalgic of the past, allowed them to remain. Henceforth their magical world was that of the sidh, the prehistoric burial mounds of Ireland. And therein lie the origins of later and contemporary folk-tradition centred on the fairies.
The Irish gods do not emerge as gods in the usual meaning of the term. They are neither worshipped nor sacrificed to. They are supernatural beings with magical powers. This, of course, is the result of Christian censorship. The greatest of all the gods is the Dagdá, ‘the good god, not good in a moral sense but ‘good at everything (ruad ro-fhessa or ‘lord of perfect knowledge), an excellent god, also called Eochaid Ollathair (father of all). He had powers of wizardry, and led the Tuatha Dé Danann into Ireland against the Fir Bolg. In this the first Battle of Moytura the high king Nuada (the Nodons of Lydney - cf above, p. 167) lost his right arm, and was borne from the field. The Fir Bolg made a compact with the Tuatha Dé Danann and the Fomori, and henceforth occupied Connaught and the outer islands.
The Dagdá was the father of Brigid, banfile (‘female poet), and of the Mac Óc (‘the young god). His club was so weighty that it had to be borne on wheels, and it slew nine men at one  stroke. He had also a harp which could play three airs - the sleep strain, the laughter strain, and the griefstrain. He had a cauldron of abundance which no one could leave without being satisfied. The bronze cauldron is a distinctive artifact of the Late Bronze Age in Ireland. The Dagdás cauldron was made the subject of satire in the Second Battle of Moytura, where the Fomori, the enemies of the Tuatha Dé Danann, prepare for him a stupendous porridge in his cauldron (another tradition has it that the porridge was to be eaten from a huge hole in the ground), with its vast ladle, and the Dagdá is invited to eat it all on pain of death; but having swallowed it all he even scrapes the bowl with his fingers. His attributes are typical of many Celtic deities in that they were not restricted to any one particular aspect of life. He was a true father-figure. His coarse appearance and his archaic club strongly suggest that here is an echo of a cult of an earlier god whose worship and affection had been strong enough to survive the arrival of more sophisticated incomers.
The text of the Second Battle of Moytura is believed to be older than that of the First Battle . It has only been preserved in a manuscript of as late as the sixteenth century; but the language is early, probably as early as the ninth century, and the tradition is pre-Christian. By way of introduction we are told that the Tuatha Dé Danann had learned magic and wizardry in the Northern Isles, and thence they had brought the spear of Lugh, which was all-conquering, and the sword of Nuada, which was an infallible weapon, and the Dagdás magic cauldron. In the Second Battle of Moytura all the gods are assembled together to fight for the reclamation of Ireland from the older gods, the Fomori, who had ruled it before the Tuatha Dé Danann. Their king is Bres, son of Elatha, whose father was a Fomor, but whose mother is of the Tuatha Dé Danann - an interesting hint both of earlier matrilinear succession and of conflict and accommodation between conflicting cults. Bres, however, is not a good king. Under him the Irish are heavily oppressed by  the Fomori, and he has allowed the Tuatha to do menial service for them. Moreover, he neglects the poets, and he is stingy, and when guests come to him he does not grease their knives, and their breaths do not smell of ale. Finally the Tuatha demand his abdication. The Fomori depart to the isles and both sides prepare for war.
The god Lugh comes to the court of the Tuatha Dé Danann and demands entrance. The door-keeper asks him first to name his qualifications, ‘for no one enters Tara without an art. Lugh claims, in turn, that he is a carpenter, a smith, a champion, a harper, and other things. Finally, he is put to the test in a game of chess, and when he is victorious Nuada admits him and entrusts him with the defence of Ireland, for he himself is disqualified by the loss of his arm. Lugh sends the Dagdá to the Formori to ask for a truce, to which they agree, but they make the Dagdá look ridiculous by forcing him to eat an immense meal of porridge (cf p.171 above). While the preparations for the battle are going forward the story-teller skilfully introduces us to all the gods of the Tuatha Dé Danann by enumerating their contributions to the fight. Goibniu the smith can offer weapons which shall never fail; Diancécht the physician, who has already made an all-purpose arm of silver for Nuada (hence his epithet Argatlám), will cure every wounded man on the day following so that he shall be made whole; Credne the brazier will supply rivets for the spears, hilts for the swords, and bosses and rims for the shields. The Dagdá adds the climax by promising that the bones of the Formori under his club shall be as hailstones under the feet of herds of horses. In the battle which follows, Lugh succeeds in casting a stone from his sling which knocks out the evil eye of their king Balor through the back of his head, slaying thereby twenty-seven of the Formori, and the rest flee to their ships. The slain are as many as the stars of heaven, the sands of the sea, the flakes of snow, the drops of dew upon the grass, and crested waves of storms. The Fornorl flee to their islands, and henceforth Ireland belongs solely to  the Tuatha Dé Danann. This story owes much to the fact that it introduces us to practically all the Tuatha Dé Danann, and tells us also of their individual prowess.
Of the purely native Irish gods who are not known outside Ireland, it is natural to think first of the chthonic gods, especially as they occur most often in the heroic sagas. These are most commonly associated with the great prehistoric tombs of the Neolithic period such as the tumuli of the ancient dead in the valley of the Boyne, known as Brugh na Bóinne, unless the name may be taken to refer specifically to Newgrange, one of the most imposing tombs of the group. Brugh na Bóinne was the home of the Mac Óc or Aengus Óc, the Dagus son by the wife of Elcmar. The Dagdá himself had no local habitation. He was ubiquitous, and the nearest thing the Irish have to a universal god, though he was often subordinate to Lugh. The association with mounds is widely attested. We have the god Midir whose dwelling was at Bri Léith in Co. Longford, and the Bodb whose sidh (or supernatural dwelling) is beyond Feimhin in Co. Tipperary in Munster. But association with springs is also attested. The source of all wisdom and knowledge is the well of Segais, at the source of the Boyne; those who ate of the hazel-nuts which grew beside it, or drank the imbas (‘inspiration) from them became inspired with the seers gift of poetry and prophecy.
We have an early story in which Aengus, the Mac Óc, in his dwelling at the Brugh has a dream of a lovely girl, and falls into a wasting sickness for lovd of her. His father and mother, the Dagdá and Boann (the goddess of the Boyne itself), make inquiries on all hands for the girl, but in vain. At last they inquire of Bodb, ‘the king of the sidh of Munster, and he ultimately finds her. She is Caer, the daughter of Ethal Anbhuail from the sídh in Connaught. The Dagdá and his companions set out with three chariots to Connaught where they spend a full week as the guests of Alill and Maeve, who ask them why they have come, and Ethal Anbhuail is forced to come out of his sídh and reveal  how his daughter may be ensnared. She is on Loch Bél Dragon in the shape of a bird, with three times fifty swans round her with silver chains and curls of gold about their heads.
Among the oldest of the stories of the Irish gods are stories of rebirth. These are all concerned with the god Manannán mac Lir who does not appear to be directly connected with the Dagdá or the gods of his circle, but is pictured as approaching Ireland from overseas or across a lake. His name is commemorated in that of the Isle of Man, but no ancient stories survive from this island. Beliefs connected with Manannán were still sufficiently tenacious in the seventh century A.D. for a claim to be put forward that Mongin, an Ulster princeling, was his son. Manannán is, moreover, generally identified with Manawydan fab Llyr of the Welsh Mabinogion, so we must associate him with the Irish Sea. Lir is an Irish god who dwelt on the cliffs of Co. Antrim, and his children, three sons and a daughter, are told of in a later Irish saga of the fifteenth century known as The Fate of the Children of Lir.
One of the most beautiful of all the stories of rebirth connected with Manannáin tells of Étain, the wife of Eochaid (or Eochu) Airem, king of Tara, and of her relationship with Midir, Manannáns fosterling, and the owner of the sídh of Bri Léith, Co. Longford. Étain had been the wife of Midir, but she was changed by his former wife, Fuamnach, out of jealousy, into a butterfly ‘that finds its delight among the flowers, and she flew  about the world until she finally came to the house of Midirs fosterling, Aengus mac Óc. He makes a glass bower for Étain, and carries it about with him wherever he goes, and there each night she sleeps beside him, and she becomes fair of form for the bower was filled with marvellously sweet-scented shrubs, and it was upon these that she thrived, upon the odour and blossom of the best of precious herbs. But the jealousy of Fuamnach lures Aengus from his dwelling, and then she blows a blast which carries Étain out of her bower over Ireland until finally she falls through the smoke-hole of the roof of the house of Étar the Warrior, and into the cup of his wife, who swallows her and bears her as a human daughter, Étain. And Étar nourishes her as his own daughter.
A certain king, Eochaid Airem, is seeking a wife, and he sends his messengers throughout Ireland upon that quest. One day Étain, the daughter Étar, sees a horseman approaching.
(A description such as this recalls not only the observation of Ammianus Marcellinus that the Gauls have always been very particular about their appearance, but also the plentiful archaeological evidence of personal adornment.) The king falls in love with the maiden and he seeks speech with her: ‘Whence art thou sprung, O maiden, says Eochaid, ‘and whence is it that thou hast come? ‘It is easy to answer that, says the maiden. ‘Étain is my name, the daughter of the king of Echrach; out of the sídh am I. The king pays her bride-price and brings her to Tara, where a fair and hearty welcome is accorded to her. 
Eochaids brother Alill subsequently falls in love with Étain, and falls into a wasting sickness for her; but in shame he tells no one the source of his illness. It is necessary that as king, Eochaidh should go for a year on a circuit of Ireland, and he leaves Étain in charge of his brother, Alill. At last Étain divines the cause of his sickness, and to relieve him makes a tryst with him, but for three successive nights Alill sleeps instead of keeping the tryst. In his place comes a strange man in Alills likeness, but Étain realizes that he is not Alill. Then the man confesses that he is mi reality Midir of Bri Léith whose wife Étain had been long ago, though later separated by the jealousy of Fuamnach. But Étain refuses to go with him unless Eochaid allows it. Eochaid finally returns, Midir comes too, steals Étain and hides her in his sídh of Brí Léith. Eochaid and his men march there, destroy it and rescue Étain. She returns to Eochaid, ‘and then she had all the worship that a king of Ireland can bestow, fair wedded love and affection such as was her due from Eochaid Airem. A picturesque account tells how Midir got possession of Étain, although Eochaid took all possible precautions to prevent his access. One night in the banqueting ban Midir was seen standing before the company in the centre of the palace.
He puts his weapons into his left hand, the woman beneath his right shoulder and he carries her off through an opening in the roof When the company stand up around the king, they see two swans circling around Tara. In this way Midir and Étain escape.
The supernatural world which forms the setting of many  tales, such as that of Étain, is rarely varied, but it is not described in detail. It is always a land of perpetual youth, where no one ever grows old or sick or dies; where flowers are always in bloom in a meadow, where young lambs frolic, and peace and goodwill reign perpetually. At times it is connected with truth-telling, but this is a specialized form. When Manannán mac Lir meets Bran in mid-ocean (cf p.281, below) he makes, by his magic, the sea appear as a flowery plain, and the fish become lambs. Even when we pass some time in this supernatural realm, as in the saga of the Sick-Bed of Cú Chulainn, the description is quite general and does not really change. This is Manannáns world, the land of the ‘ever young, Tir na n-Óc, which may be compared with the Odainsaler (‘the land of immortality) of Old Norse mythology; Manannáns people, like Guthmandr in the Old Norse sagas, ‘do not die, but live from generation to generation. In this land of youth, perhaps, we are given a glimpse of Celtic beliefs and hopes regarding the afterlife.
In one early cycle of sagas we get a more intimate glimpse of the supernatural world. The earliest story occurs in the cycle of the ‘high king, Conn Cétchathach (‘of one hundred battles), the grandfather of Cormac mac Airt, and probably dates from the eighth century. As Conn stands at dawn on the ramparts of Tara with his three druids and his fili, they are turrounded by a mist from which a horseman emerges. The horseman greets Conn and invites him and his entourage to go with him to his dwelling. They come eventually to a plain where there is a golden tree and a house with a golden ridgepole. Inside is a girl seated on a crystal chair and wearing a gold cirown. Close to her are a silver vat, a vessel of gold and a golden cup. Lugh himself is there, seated on his throne. He tells them that lie has come back ‘after death to tell Conn the length of his reign and of all his successors. The girl is the ‘Sovereignty of Ireland and as she serves Conn with meat and ale she asks Lugh name of every one in turn and his fili writes them down in  ogam on staves of yew. Then the scál (Lugh) and his house disappear, but the vat and the vessel and the staves of yew remain with Conn.
The experiences of Conn and his family are all connected with the supernatural world. His son, Conla, is enticed away from him by a supernatural maiden and goes with her to the supernatural land for ever; but we are not told anything more about it. Conlas brother, Art Aenfer ('Art the Solitary), is also beloved of a woman of the Tuatha Dé Danann. but there is no ancient version of this tale. The Echtrae Conli , however, relates a story of Cormac, Conns grandson, which has much in common with that of Conns.
The story opens, like Conns, with a picture of the king alone one May dawn on the ramparts of Tara when he sees a warrior approach. He is finely dressed, like all Irish supernatural beings, and he carries on his shoulder a branch with three golden apples, which when shaken give forth delightful music, such as might put the sick and wounded to sleep. Cormac asks him whence he has come. The reply is characteristic: ‘From a land where there is only truth, said he, ‘and there is no old age, nor decay, nor sadness, nor envy, nor jealousy, nor hatred, nor arrogance. They swear friendship together, and the warrior gives the branch to Cormac in exchange for three wishes, which are to be granted at Tara. Cormac returns to the palace and all admire the sleep-inducing branch, but after a year the warrior comes and takes away as his three wishes Cormacs son and,, daughter and wife. Cormac pursues him and a great mist falls and Cormac finds himself alone in the midst of a wide plain, where he sees a fort with defences of bronze. Passing through a series of enclosures he enters a beautiful palace with a shining spring surrounded by hazel trees, and salmon in the spring are eating the hazel nuts as they fall from the trees. We are here at the Spring of Inspiration.
Within the palace a handsome warrior and a beautiful girl welcome him, and the pig for the evening meal is duly cooked.  Then Cormac: tells how his family has been taken from him, and the warrior chants a lullaby so that Cormac sleeps. On awaking his retinue and his reunited family stand around him. A beautiful gold cup is brought to the warrior which has the quality of breaking into three parts when three lies are told over it, but of becoming whole again when three truths are told. The cup is made whole when the warrior says that Cormacs son has not seen a woman, neither has his wife nor daughter seen a man since leaving Tara. For the warrior then reveals that he is Manannán mac Lir who has brought Cormac to see the Land of Promise. When Cormac wakes next morning he finds himself with his family on the grass at Tara with the branch and the cup.
It will be seen that an early Irish tradition or traditional ritual connected with the high kings of Tara, from Conn Cétchathach onwards for several generations, has been utilized by later saga tellers as a framework for various purposes - for history as told by the poetic inspiration in the case of Conn himself, for the moral purpose in the case of Cormac, Lugh and Manannin are interchangeable, but the identity of the general framework will be recognized. It is interesting to note also how both here and in the other stories of this family the woman is always the means by which the god of rebirth, the scál, expresses himself.
It would be unreasonable to seek within the whole corpus of early Irish literature a coherent summary of the beliefs of the Celts as such. Nothing even remotely comparable with the modern concept of ‘theology emerges, nor should one be expected, particularly when one considers the circumstances in which these oral traditions were first written down. Yet when read critically. this often beautiful literature may reveal much that is relevant to a modern appreciation of early Celtic religion. Concessions to Christianity were slight, and in the main consisted in obscuring where necessary the divinity of the principal characters in the myths. The supernatural, however.  is everywhere evident, particularly in that pertaining to the Tuatha Dé Danann. For these surely were the gods of the Celts in Ireland. Most peoples create their gods according to their own mortal needs, ideals and aspirations, and in the Tuatha may be glimpsed something of the manner in which La Tène Celts in Ireland may have pictured the ideal life. Celtic society and particularly its social obligations, such as delight in hospitality, are here transferred to the idealized world of the supernatural. The superior powers of the Tuatha were perhaps thought to have been available to their devotees.
There can be no certainty that whatever attitudes towards religion may be revealed in the early Irish literature of the Celts in Ireland were necessarily shared by continental Celts. Yet the appearance of Lugh in the literature and his commemoration, perhaps as a tutelary deity, in Celtic place-names from Lyons to Carlisle, hint at that elusive element of underlying unity of befiefreferred to at the beginning of this chapter. What may be deduced of Celtic gods as they appear in the literature, however, tends to confirm the inference derived from a study of archaeological evidence and comments by classical authors that these gods and goddesses neither possessed restricted attributes, nor exercised circumscribed powers. One of Lughs epithets, for example, was Samíldánach (‘many-skilled - cf above, p. 172), and the Dagdá was Ruad Ro-fhessa (‘lord of perfect knowledge) . Few of the presumptive deities of Irish literature may he identified either in Romano-Celtic inscriptions or in classical authors, but this serves to emphasize that the Celts in their individualistic fashion chose to worship local divinities.
Irish literature is, not unnaturally, obscure as to ritual observances as such, although there are references to what may be interpreted as various activities including ritual races, ordeals (sometimes preceding the inauguration of kings) and sacrifice. The persistent recurrence in the literature of certain days in die year on which particularly important events took place makes it possible to identify the four major peaks of the Celtic ritual  calendar. This is reinforced by later folk-tradition, particularly that concerning Lugnasadh, and Christian attempts to efflace pagan practice by adopting and adapting to Christian usage well-established cult-practices, as in the case of Imbolc. Samhain (1 November) was the beginning of the Celtic year, at which time any barriers between man and the supernatural were lowered. Imbolc followed on 1 February. This appears to have been involved primarily with fertility ritual, traditionally associated with the lactation of ewes. Christianity, in an attempt to reconcile the strong attraction of this feast with its own teaching and ritual, made it the feast of St Brigid, who in Irish Christian tradition was made the midwife of the Virgin Mary. St Brigid herself, if she ever existed, appears to have taken over the functions of a Celtic goddess of the same name and comparable attributes. Beltine (or Beltaine) was celebrated on 1 May, a spring-time festival of optimism. Fertility ritual again was important, in part perhaps connecting with the waxing power of the sun, symbolized by the fighting of fires through which livestock were driven, and around which the people danced in a sunwise direction. 1 August was Lugnasadh, the festival of the ubiquitous Lugh, more than a strong echo of which survives even today in Ireland and other parts of the earlier Celtic world. Emphasis on stock-rearing, appropriate to what is known of Celtic economy in Ireland, is apparent in these celebrations, which seemingly took little account of a solar calendar centred on solstices and equinoxes.
In concluding this survey of Irish mythology, I would call attention to the naturalness with which men, women and the gods meet and pass in and out of the natural and the supernatural spheres. In many circumstances there does not seem to have been any barrier. At times a ‘druidical mist surrounds the hero and heralds the approach of the god; at others the god appears from across the sea and perhaps a lake; sometimes a human being enters a sídh or burial mound, either as a human being or as a bird; but normally the two-way traffic between the  natural and the supernatural is open. In general, however, though by no means invariably, return to the land of mortals is difficult and sometimes impossible for mortals who have visited the abode of the dead.
A beautiful dignity hangs over Irish mythology, an orderliness, a sense of fitness. All the gods are beautifully dressed and most are of startlingly beautiful appearance. It is only by contrast with other mythologies that we realize that the ‘land of promise contains little that is ugly. There is no sin and no punishment. There are few monsters, nothing to cause alarm, not even extremes of climate. There is no serious warfare, no lasting strife. Those who die, or who are lured away to the Land of Promise, the land of the young, leave for an idealized existence, amid beauty, perpetual youth, and goodwill. The heathen Irish erected a spirituality - a spiritual loveliness which comes close to an ideal spiritual existence. [...; &c.]