SÍDH . Various occasional titles are used to designate the otherworld in early Irish, but the normal generic term for it is sídh (pl. sídhe ). Its common currency in this sense is confirmed, if that were necessary, by the fact that it was borrowed by the author of the Old Welsh poem Preideu Annwn (The spoils of Annwn). The poem tells of a raid by Arthur and three shiploads of his followers on the otherworld stronghold of Kaer Sidi (from the Old Irish genitive sídhe ) with the aim of carrying off the magic caldron of abundance which belonged to the lord of the otherworld. Annwn is a common term in Welsh for the otherworld, conceived in this instance as somewhere reached after a journey by boat but more generally described as somewhere beneath the ground. Similarly the Irish otherworld, whether designated by sídh or by another word, is occasionally envisaged as being overseas but much more frequently as being underground.
It is said that when the Gaels (the Irish Celts) came to Ireland and defeated the divine Tuatha Dé Danann, their poet and judge Amhairghin decreed that Ireland be divided in two and that the underground half be given to the Tuatha Dé Danann and the other half to the Gaels. So it was done, and the Daghdha, the senior of the gods, assigned to each of the chiefs of the Tuatha Dé his own fairy dwelling. As Marie-Louise Sjoestedt has commented, this division "marks the end of the mythical period when the supernatural was undisputed master of the earth, and the beginning of a new period in which men and gods inhabit the earth together. From that moment the great problem of religion becomes important, the problem of the relationship between man and the gods" (Gods and Heroes of the Celts, London, 1949, p. 47).
But while the otherworld was generally associated with the subterranean regions, it was not confined to them. Transcending as it did the limitations of human space as well as time, its location was perceived with considerable flexibility: it could be under the sea as well as under the ground, in nearby or distant islands, in houses which may disappear as suddenly as they first appeared, or it could be coextensive with the secular world. It could be reached through a cave, the waters of a lake, a magic mist, or simply through the acquisition of heightened insight. But it was not merely a spiritual world, which is presumably why the creators of Celtic mythic narrative sought in many instances to give it a clear geographic identity: Lucan in his Pharsalia (5.452) wrote that the continental Celts had no fear of death since it was for them only the middle of a long life. According to him, their druids taught them that after death human souls continued to control their bodies in another world (alio orbe ); mutatis mutandis, this would also be a fair summary of the view of the afterlife implicit in early Irish and Welsh tradition.
Very frequently in Irish tradition the subterranean location of the otherworld is identified with certain hills and mounds, whether natural or manmade—so much so, in fact, that the word sídh commonly means simply "fairy or otherworld hill," in other words, an ordinary hill, usually modest in size, within which a whole world of supernatural beings live their own varied lives. Sometimes the sídh is a megalithic burial mound, as in the case of the great tumulus of Newgrange at Bruigh na Bóinne, which was pre-Celtic but was assimilated to Gaelic mythology and considered to be the home of the god Mac ind Óg, the Irish equivalent of British and continental Celtic Maponos. The related Welsh term, gorsedd ("mound"), had similar supernatural associations, though these are less fully or clearly documented. But evidently this denotation of "hill" was not the primary meaning of *sedos, the Celtic form from which Irish sídh derived. Based on the Indo-European root sed- ("sit"), its semantic evolution seems to have moved from "residence in general" to "residence of the gods," that is, the otherworld, and then to those hills within which the gods were believed to reside. Nor does its evolution end there, for by semantic transference Irish sídh came to refer also to the supernatural beings who inhabit the sídh residence, and in modern spoken Irish the generic term for an otherworldly being or fairy is sídheog, the diminutive of sídh.
Carey, John. "The Location of the Otherworld in Irish Tradition." Éigse 19 (1982): 36–43. Seeks to demonstrate that the overseas location of the otherworld was not part of the indigenous tradition. The point is well argued, if not wholly proven.
Nutt, Alfred. "The Happy Otherworld in the Mythico-Romantic Literature of the Irish." In The Voyage of Bran, Son of Febal, to the Land of the Living, edited by Kuno Meyer and Alfred Nutt, vol. 1, pp. 101–332. London, 1895.
Ó Cathasaigh, Tomás. "The Semantics of 'síd.'" Éigse 17 (1977–1978): 137–155. Examines the generally accepted identity of sídh ("otherworld [hill]") and sídh ("peace") and explores its implications in terms of the relationship between sacral kingship and the supernatural powers.
Proinsias Mac Cana (1987 and 2005)