Nothing about the Celts is more certain than that they believed in a life after death. On this the testimonies of archaeology, classical commentary and insular tradition are essentially at one. The grave furniture which accompanies Celtic burials presupposes such a belief, classical authors make explicit statement of it, and insular storytellers have woven it imaginatively into the fabric of their literature.
That this belief was part of the formal teaching of the Gaulish druids is confirmed by virtually every classical author who has written of the Celts. Caesar, like the good pragmatist that he was, takes the consequence for the cause and assumes that the object of the druids in preaching the immortality of the soul was to ensure that their followers, through disregard of death, would be the more valorous in war. According to others, for Caesar is ambiguous on this point, the druids taught that the soul passed from one body to another, and this they relate specifically to the Pythagorean theory of metempsychosis, or transmigration of souls. The idea has an obvious attraction and it is still not infrequently echoed by modern writers on the druids, though the actual evidence for it is unconvincing. It is true that in Irish and Welsh literature shape-shifting is common place, and there are even a number of instances of characters undergoing a prolonged series of metamorphoses mention has already been made of Fintan, sole survivor of the first invasion of Ireland, and of the swineherd antecedents of the divine bulls of Táin Bó Cuailnge, and Welsh tradition has a worthy parallel to these in the mythical Taliesin (as opposed to his historical counterpart), who by his own boast had undergone countless transformations and was as old as the worlds history but this is something quite different to Pythagorean metempsychosis or to the samsara of Hindu belief. Far from implying that the process of serial reincarnation affected all animate beings, these legends restrict it to a relatively small number of instances, all of them concerning either deities or mythical personages. Assuming, however, that similar legends were current among the Gaulish Celts, it can be readily appreciated that they would have lent themselves to misinterpretation by classical commentators familiar with the Pythagorean theory.
But the classical sources also contain allusions to a different concept of immortality among the Celts. Lucan in his well-known apostrophe to the druids attributes to them the teaching that after death mens souls continue to control their bodies in another world (orbe alio), which is not the silent abode of Erebus or the deep and pallid realm of Dis. Therefore, he adds, the Celts accept death without trepidation since it is for them only a juncture in a long life. This otherworld of corporeal beings which Lucan contrasts with the gloomy classical underworld peopled by pale insubstantial shades evidently corresponds to the preternatural world which figures so largely in the traditions of the Irish and the Welsh.
This otherworld of the insular Celts is a changing scene of many phases, and if ones mind instantly conjures up an image of an Elysian land where men and women live in unending happiness, the explanation may well be that this particular image of the otherworld was handled repeatedly and with remarkable sensitivity by a succession of monastic lyric poets and storytellers from the seventh century onwards. Certain features recur continually in their descriptions of it. It is The Land of the Living, Tír inna mbeo, where sickness and decay are unknown. It is a land of primeval innocence where the pleasures of love are untainted by guilt. Its women are numerous and beautiful and they alone people some of its regions, so that then it becomes literallyThe Land of Women, Tír inna  mban. It is filled with enchanting music from bright-plumaged birds, from the swaying branches of the otherworld tree, from instruments which sound without being played and from the very stones. And it has abundance of exquisite food and drink, and magic vessels of inexhaustible plenty. The woman who comes to invite Bran mac Febhail on his wondrous voyage there pictures it first as an island, but later as three times fifty distant isles, far to the west of Ireland:
Another poem of the invitation-type mentions briefly the paradisiac communism of unending abundance and exemplifies the sensuous use of colour which marks early Irish lyric verse in general and especially the descriptions of the blissful otherworld:
This world transcends the limitations of human time; the mortal returning from a visit there may suddenly become aged and decrepit on contact with the material world, or he may simply dissolve into dust. It also transcends all spatial definition. It may be situated under the ground or under the sea; it may be in distant islands or coextensive with the world of reality. It may be a house or a palace that appears and disappears with equal suddenness, or it may be a little grass-covered hill that encompasses a whole vast and variegated world with its peoples. It may be reached through a cave, through the waters of a lake, through a magic mist or simply through the granting of sudden insight.
It is conceived as a land of peace and harmony, yet its inhabitants do not have to forego the principal diversion of  heroic society, namely fighting. And what is more remarkable perhaps, their internal conflicts can be decided in favour of one side or the other by the intervention of a human being - a favourite motif in Irish, both in the early literature and in the modern folklore, and one which occurs also in the Welsh tale of Pwyll. In The Wasting Sickness of Cú Chulainn the Ulster hero is asked to aid Labhraidh of the Swift Sword-hand against his enemies for the space of one day, in return for which he is promised the love of the beautiful Fann. In Echtrae Laeghairi, The Adventure of Laeghaire, a man emerges out of a mist before Crimhthann Cass, king of Connacht, and seeks his help in recovering his wife who has been abducted and whom he has failed to win back in battle. Laeghaire, Crimhthanns son, sets out with a force of fifty men in the wake of their supernatural visitant, and they duly overcome his enemies and recover his wife. Unlike Cú Chulainn, however, Laeghaire only returns to his fathers kingdom to bid a last farewell; he and his men have taken wives from among the women of Magh Dá Cheo, The Plain of the Two Mists (one of the many evocative names given to the Irish otherworld), and they decide to remain there secure from the anxieties and infirmities of the mortal world.
And though it may seem strange that the happy folk of this Gentle Land should pass some of their many idle hours in mutual slaughter, this is really only a minor manifestation of the general fluidity, or ambivalence, which characterises the Celtic otherworld. Being, as it is ultimately, an imaginative reflex of human attitudes and aspirations, this other kingdom assumes different forms according to the occasion and circumstance, but these forms are not sharply or consistently distinguished. When a mortal visits the otherworld by invitation, it is usually pictured as a land of contentment and joy. But when it is invaded by human heroes - a favourite theme in storytelling and one which is related to Cú Chulainn, Fionn and Arthur among others then it wears a very different image. It may still be a country of riches and of wonders - and frequently the declared object of such heroic expeditions is to seize its treasures and its magic talismans -but inevitably its status relative to mankind has been transformed: its rulers and its welcoming hosts are now formidable and even monstrous enemies, fit to test the mettle of the greatest hero. In one tale Cú Chulainn himself recounts an expedition of his to the Land of Shade. He found there a fortress surrounded by seven walls, and on each a palisade of irons on which were fixed nine heads. Hordes of serpents and other terrifying monsters were sent against him and his followers, but he slew them all, stormed the stronghold and carried off its treasures. In contexts of this nature the hero moves in a region of perilous adventure and of fearsome, malignant beings. The main emphasis is on the hazards he faces, on the dreadful ingenuity and magic which his supernatural foes have at their command and on all the awesome trappings -swordbridges, revolving castles, &c. -which characterise Irish and Welsh tales of the all but impregnable otherworld and which later become part of the routine paraphernalia of Arthurian romance.
The Feast of Samhain
On the eve of Samhain Ailill and Medhbh, king and queen of Connacht, offer the prize of his choice to whomsoever succeeds in putting a withe around the foot of either of two captives who had been hanged the previous day. Nera alone accepts the challenge. He goes to the gallows but he only succeeds in fixing the withe after the corpse has instructed him. The corpse then complains of thirst and Nera carries him on his back to a dwelling in which he finds water. Having replaced him on the gallows he returns to the royal court of Cruachain only to find it in flames and the severed heads of its people near by. As the attacking warriors move off Nera follows them into the Cave of Cruachain, a famous gateway to the otherworld. Once inside the sídh he is discovered but is permitted to remain. He takes a wife from among the women of the sídh and from her he learns that his vision of the destruction of the court of Cruachain was but a premonition: it will come true next Samhain, however, unless the sídh is ravaged before then. He sets out to bring warning to his own people, carrying with him fruits of summer- wild garlic and primrose and golden fern - to prove whence he had come, and he finds his friends still seated around the cauldron as he had left them, though much had befallen him in the meantime. When Samhain returns the Connacht warriors invade and plunder the sídh and carry of the three great treasures of Ireland. But Nera remains behind with his family in the sídh and there he will stay until Doomsday.
The legends of Samhain are legion. Muirchertach mac Erca and Crimhthann mac Fidhaigh perish through the sorcery of supernatural women, Cú Chulainn is visited by Lí Ban and Fann, and it is then that the great mythic battle of Magh Tuiredh is enacted. Constituting as it does a partial return to primordial chaos, Samhain is the appropriate setting for myths which symbolise the dissolution of established order as a prelude to its recreation in a new period of time. Famous kings and heroes die at Samhain - Muirchertach, Crimhthann, Diarmaid mac Cerbhaill, Conaire Mór, Cú Chulainn and others - sometimes within an elaborate scenario which is strongly redolent of ritual. It is a time of unbridled carousal, and the element of chaos and turbulence which is inherent in the feast emerges clearly in the story of Mesca Ulad, The Intoxication of the Ulstermen. Faced with two invitations to go feasting, honour demands that the Ulstermen accept both. And so, having indulged themselves lavishly during the first half of the night at the court of Dún Dá Bhenn (in the present Co. Derry), they then set out  for a second session at Cú Chulainns fort of Dún Delga. They lose themselves en route and career headlong on a wild and drunken course throughout the length of Ireland, finally to arrive among their Munster enemies who first proceed to feast them and then all but succeed in roasting them alive in a burning house.
The land of the dead
The general structure of the poem suggests the common notion of the otherworld as an island, but it is named by several different titles and described in terms which imply quite disparate conceptions of its character. In one stanza it appears as a kind of twilight underworld - as it does later in the Latin works of Walter Map and Giraldus Cambrensis - and once it is even referred to as uffern, Hell, showing early confusion with the Christian otherworld. In another stanza it becomes Caer Wydyr, Fortress of Glass, from whose sentinel Arthur and his company found it difficult to obtain response. This recalls an episode in Nenniuss Historia Brittonum (of the early ninth century) which describes how the sons of Míl, having come to Ireland, took ship again to capture a tower of glass (turris vitrea) standing in the middle of the sea and were all of them drowned but for the crew of one ship which was unable to take part in the expedition. The occupants of the tower, when addressed, made no answer, maintaining the silence which is the specific mark of the dead in Celtic as in other traditions. Quite clearly the glass tower (which incidentally Nennius wrongly associates with the sons of Míl) and the glass fortress are one and the same and symbolise the realm of the dead.
Yet the Welsh poet did not think of Annwn solely, or primarily, as a silent land of the dead. One of the titles he gives it is Caer Feddwid, Court of Intoxication, or Carousal, and its staple drink is sparkling wine. It is also named Caer Siddi, and under this title it is described in a separate poem as a region in which sickness and old age are unknown, where there is enchanting music and a fountain flows with liquid sweeter than white wine -in other words it is The Land of the Living. How then explain this apparent inconsistency? The answer is doubtless to be found in the early Irish Voyage tales which picture the otherworld as an archipelago of islands of varying and sometimes contrasting character which the intrepid mortal visits severally on his long Odyssey. For though the Welsh poem does not suggest that Arthurs exploit was another extended exploration of the supernatural, like Brans or Mael Dúins, nonetheless it is clearly a composite picture comprising just such a series of separate realisations of the otherworld as are found in these Irish Voyages. And the significant thing is that our poet, while obviously aware of their disparity, saw no inconsistency in conjoining the land of the dead and The Land of the Living as two aspects of the same otherworld.
It should perhaps be added that this underlying unity has not been universally accepted by modern scholars. It has sometimes been pointed out that those whom Irish (and indeed Welsh) literature records as visiting the otherworld are either heroes or kings, and the conclusion is drawn that the people at large must have shared a less distinguished afterlife - in the land of the dead. The flaw in this argument is its disregard for the fact that the early Celtic literatures are preponderantly aristocratic with an infinite capacity for ignoring the fortunes of the masses, whether in this life or in another. In fact, there is no good reason to suppose that the men and women of early Ireland thought very differently about these matters from their descendants further removed from them in time than in outlook - of whom the Elizabethan Father William Good remarked appositely: They suppose that the souls of such as are deceased go into the company of certain men, famous in those places, touching whom they retain still fables and songs.