By J. A. MacCulloch
Chapter IX from The Religion of the Ancient Celts 
THOUGH man usually makes his gods in his own image, they are unlike as well as like him. Intermediate between them and man are ideal heroes whose parentage is partly divine, and who may themselves have been gods. One mark of the Celtic gods is their great stature. No house could contain Bran, and certain divine people of Elysium who appeared to Fionn had rings “as thick as a three-ox goad.” Even the Fians are giants, and the skull of one of them could contain several men. The gods have also the attribute of invisibility, and are only seen by those to whom they wish to disclose themselves, or they have the power of concealing themselves in a magic mist. When they appear to mortals, it is usually in mortal guise, sometimes in the form of a particular person, but they can also transform themselves into animal shapes, often that of birds. The animal names of certain divinities show that they had once been animals pure and simple, but when they became anthropomorphic, myths would arise telling how they had appeared to men in these animal shapes. This, in part, accounts for these transformation myths. The gods are also immortal, though in myth we hear of their deaths. The Tuatha Dé Danann are “unfading,” their “duration is perennial.” This immortality is sometimes an inherent quality; sometimes it is the result of eating immortal food: Manannan’s swine, Goibniu’s feast of age and his immortal ale, or the apples of Elysium. The stories telling of the deaths of the gods in the annalists may be based on old myths in which they were said to die, these myths being connected with ritual acts in which the human representatives of gods were slain. Such rites were an inherent part of Celtic religion. Elsewhere the ritual of gods like Osiris or Adonis, based on their functions as gods of vegetation, was connected with elaborate myths telling of their death and revival. Something akin to this may have occurred among the Celts.
The divinities often united with mortals. Goddesses sought the love of heroes who were then sometimes numbered among the gods, and gods had amours with the daughters of men. Frequently the heroes of the sagas are children of a god or goddess and a mortal, and this divine parentage was firmly believed in by the Celts, since personal names formed of a divine name and –genos or –gnatos, “born of,” “son of,” are found in inscriptions over the whole Celtic area, or in Celtic documents–Boduogenos, Camulognata, etc. Those who first bore these names were believed to be of divine descent on one side. Spirits of nature or the elements of nature personified might also be parents of mortals, as a name like Morgen, from Morigenos, “Son of the Sea,” and many others suggest. For this and for other reasons the gods frequently interfere in human affairs, assisting their children or their favourites. Or, again, they seek the aid of mortals or of the heroes of the sagas in their conflicts or in time of distress, as when Morrigan besought healing from Cúchulainn.
As in the case of early Greek and Roman kings, Celtic kings who bore divine names were probably believed to be representatives or incarnations of gods. Perhaps this explains why a chief of the Boii called himself a god and was revered after his death, and why the Gauls so readily accepted the divinity of Augustus. Irish kings bear divine names, and of these Nuada occurs frequently, one king, Irél Fáith, being identified with Nuada Airgetlam, while in one text nuadat is glossed in ríg, “of the king,” as if Nuada had come to be a title meaning “king.” Welsh kings bear the name Nudd (Nodons), and both the actual and the mythic leader Brennus took their name from the god Bran. King Conchobar is called día talmaide, “a terrestrial god.” If kings were thought to be god-men like the Pharaohs, this might account for the frequency of tales about divine fatherhood or reincarnation, while it would also explain the numerous geasa which Irish kings must observe, unlike ordinary mortals. Prosperity was connected with their observance, though this prosperity was later thought to depend on the king’s goodness. The nature of the prosperity–mild seasons, abundant crops, fruit, fish, and cattle–shows that the king was associated with fertility, like the gods of growth. Hence they had probably been once regarded as incarnations of such gods. Wherever divine kings are found, fertility is bound up with them and with the due observance of their tabus. To prevent misfortune to the land, they are slain before they grow old and weak, and their vigour passes on to their successors. Their death benefits their people. But frequently the king might reign as long as he could hold his own against all comers, or, again, a slave or criminal was for a time treated as a mock king, and slain as the divine king’s substitute. Scattered hints in Irish literature and in folk survivals show that some such course as this had been pursued by the Celts with regard to their divine kings, as it was also elsewhere. It is not impossible that some at least of the Druids stood in a similar relation to the gods. Kings and priests were probably at first not differentiated. In Galatia twelve “tetrarchs ” met annually with three hundred assistants at Drunemeton as the great national council. This council at a consecrated place (nemeton), its likeness to the annual Druidic gathering in Gaul, and the possibility that Dru– has some connection with the name “Druid,” point to a religious as well as political aspect of this council. The “tetrarchs” may have been a kind of priest-kings; they had the kingly prerogative of acting as judges as had the Druids of Gaul. The wife of one of them was a priestess, the office being hereditary in her family, and it may have been necessary that her husband should also be a priest. One tetrarch, Deiotarus, “divine bull,” was skilled in augury, and the priest-kingship of Pessinus was conferred on certain Celts in the second century B.C., as if the double office were already a Celtic institution. Mythic Celtic kings consulted the gods without any priestly intervention, and Queen Boudicca had priestly functions. Without giving these hints undue emphasis, we may suppose that the differentiation of the two offices would not be simultaneous over the Celtic area. But when it did take effect priests would probably lay claim to the prerogatives of the priest-king as incarnate god. Kings were not likely to give these up, and where they retained them priests would be content with seeing that the tabus and ritual and the slaying of the mock king were duly observed. Irish kings were perhaps still regarded as gods, though certain Druids may have been divine priests, since they called themselves creators of the universe, and both continental and Irish Druids claimed superiority to kings. Further, the name σεμνοθέοι, applied along with the name “Druids” to Celtic priests, though its meaning is obscure, points to divine pretensions on their part.
The incarnate god was probably representative of a god or spirit of earth, growth, or vegetation, represented also by a tree. A symbolic branch of such a tree was borne by kings, and perhaps by Druids, who used oak branches in their rites. King and tree would be connected, the king’s life being bound up with that of the tree, and perhaps at one time both perished together. But as kings were represented by a substitute, so the sacred tree, regarded as too sacred to be cut down, may also have had its succedaneum. The Irish bile or sacred tree, connected with the kings, must not be touched by any impious hand, and it was sacrilege to cut it down. Probably before cutting down the tree a branch or something growing upon it, e.g. mistletoe, had to be cut, or the king’s symbolic branch secured before he could be slain. This may explain Pliny’s account of the mistletoe rite. The mistletoe or branch was the soul of the tree, and also contained the life of the divine representative. It must be plucked before the tree could be cut down or the victim slain. Hypothetical as this may be, Pliny’s account is incomplete, or he is relating something of which all the details were not known to him. The rite must have had some other purpose than that of the magico-medical use of the mistletoe which he describes, and though he says nothing of cutting down the tree or slaying a human victim, it is not unlikely that, as human sacrifice had been prohibited in his time, the oxen which were slain during the rite took the place of the latter. Later romantic tales suggest that, before slaying some personage, the mythico-romantic survivor of a divine priest or king, a branch carried by him had to be captured by his assailant, or plucked from the tree which he defended. These may point to an old belief in tree and king as divine representatives, and to a ritual like that associated with the Priest of Nemi. The divine tree became the mystic tree of Elysium, with gold and silver branches and marvellous fruits. Armed with such a branch, the gift of one of its people, mortals might penetrate unhindered to the divine land. Perhaps they may be regarded as romantic forms of the old divine kings with the branch of the divine tree.
If in early times the spirit of vegetation was feminine, her representative would be a woman, probably slain at recurring festivals by the female worshippers. This would explain the slaying of one of their number at a festival by Namnite women. But when male spirits or gods superseded goddesses, the divine priest-king would take the place of the female representative. On the other hand, just as the goddess became the consort of the god, a female representative would continue as the divine bride in the ritual of the sacred marriage, the May Queen of later folk-custom. Sporadically, too, conservatism would retain female cults with female divine incarnations, as is seen by the presence of the May Queen alone in certain folk-survivals, and by many Celtic rituals from which men were excluded.