Posted from the book “The Religion of the Ancient Celts" - By J. A. MacCulloch -  - (Obtain this full work and many more backups by clicking here!)
This book, is one of the best scholarly treatments of the ancient Celtic religion. Written early in the 20th Century, "Religion of the Ancient Celts" includes extensive treatment of that perennially fascinating subject, the Druids.
Animal worship pure and simple had declined among the Celts of historic times, and animals were now regarded mainly as symbols or attributes of divinities. The older cult had been connected with the pastoral stage in which the animals were divine, or with the agricultural stage in which they represented the corn-spirit, and perhaps with totemism.
We shall structure this study on three main aspects:1 - Traces of the older animal cults
2- Transformation of animal gods into symbols
The presence of a bull with three cranes (Tarvos Trigaranos) on the Paris altar, along with the gods Esus, Juppiter, and Vulcan, suggests that it was a divine animal, or the subject of a divine myth. As has been seen, this bull may be the bull of the Táin bó Cuailgne. Both it and its opponent were reincarnations of the swine-herds of two gods. In the Irish sagas reincarnation is only attributed to gods or heroes, and this may point to the divinity of the bulls. We have seen that this and another altar may depict some myth in which the bull was the incarnation of a tree or vegetation spirit. The divine nature of the bull is attested by its presence on Gaulish coins as a religious symbol, and by images of the animal with three horns--an obvious symbol of divinity.
On such an image in bronze the Cimbri, Celticised Germans, swore. The images are pre-Roman, since they are found at Hallstadt and La Tène. Personal names like Donnotaurus (the equivalent of the Donn Taruos of the Táin) or Deiotaros ("divine bull"), show that men were called after the divine animal. Similarly many place-names in which the word taruos occurs, in Northern Italy, the Pyrenees, Scotland, Ireland, and elsewhere, suggest that the places bearing these names were sites of a bull cult or that some myth, like that elaborated in the Táin, had been there localised. But, as possibly in the case of Cúchulainn and the bull, the animal tended to become the symbol of a god, a tendency perhaps aided by the spread of Mithraism with its symbolic bull.
A god Medros leaning on a bull is represented at Haguenau, possibly a form of Mider or of Meduris, a surname of Toutatis, unless Medros is simply Mithras. Echoes of the cult of the bull or cow are heard in Irish tales of these animals brought from the síd, or of magic bulls or of cows which produced enormous supplies of milk, or in saintly legends of oxen leading a saint to the site of his future church. These legends are also told of the swine, and they perhaps arose when a Christian church took the place of the site of a local animal cult, legend fusing the old and the new cult by making the once divine animal point out the site of the church. A late relic of a bull cult may be found in the carnival procession of the Bœuf Gras at Paris.
A cult of a swine-god Moccus has been referred to. The boar was a divine symbol on standards, coins, and altars, and many bronze images of the animal have been found. These were temple treasures, and in one case the boar is three-horned. But it was becoming the symbol of a goddess, as is seen by the altars on which it accompanies a goddess, perhaps of fertility, and by a bronze image of a goddess seated on a boar. The altars occur in Britain, of which the animal may be the emblem--the "Caledonian monster" of Claudian's poem. The Galatian Celts abstained from eating the swine, and there has always been a prejudice against its flesh in the Highlands. This has a totemic appearance. But the swine is esteemed in Ireland, and in the texts monstrous swine are the staple article of famous feasts. These may have been legendary forms of old swine-gods, the feasts recalling sacrificial feasts on their flesh. Magic swine were also the immortal food of the gods. But the boar was tabu to certain persons, e.g. Diarmaid, though whether this is the attenuated memory of a clan totem restriction is uncertain. In Welsh story the swine comes from Elysium--a myth explaining the origin of its domestication, while domestication certainly implies an earlier cult of the animal. When animals come to be domesticated, the old cult restrictions, e.g. against eating them, usually pass away. For this reason, perhaps, the Gauls, who worshipped an anthropomorphic swine-god, trafficked in the animal and may have eaten it. Welsh story also tells of the magic boar, the Twrch Trwyth, hunted by Arthur, possibly a folk-tale reminiscence of a boar divinity.
Place-names also point to a cult of the swine, and a recollection of its divinity may underlie the numerous Irish tales of magical swine. The magic swine which issued from the cave of Cruachan and destroyed the young crops are suggestive of the theriomorphic corn-spirit in its occasional destructive aspect. Bones of the swine, sometimes cremated, have been found in Celtic graves in Britain and at Hallstadt, and in one case the animal was buried alone in a tumulus at Hallstadt, just as sacred animals were buried in Egypt, Greece, and elsewhere. When the animal was buried with the dead, it may have been as a sacrifice to the ghost or to the god of the underworld.
The divinity of the serpent is proved by the occurrence of a horned serpent with twelve Roman gods on a Gallo-Roman altar. In other cases a horned or ram's-headed serpent appears as the attribute of a god, and we have seen that the ram's-headed serpent may be a fusion of the serpent as a chthonian animal with the ram, sacrificed to the dead. In Greece Dionysus had the form both of a bull and a horned serpent, the horn being perhaps derived from the bull symbol. M. Reinach claims that the primitive elements of the Orphic myth of the Thracian Dionysos-Zagreus--divine serpents producing an egg whence came the horned snake Zagreus, occur in dislocated form in Gaul. There enlacing serpents were believed to produce a magic egg, and there a horned serpent was worshipped, but was not connected with the egg. But they may once have been connected, and if so, there may be a common foundation both for the Greek and the Celtic conceptions in a Celtic element in Thrace. The resemblances, however, may be mere coincidences, and horned serpents are known in other mythologies--the horn being perhaps a symbol of divinity. The horned serpent sometimes accompanies a god who has horns, possibly Cernunnos, the underworld god, in accordance with the chthonian character of the serpent.
In the Cúchulainn cycle Loeg on his visit to the Other-world saw two-headed serpents--perhaps a further hint of this aspect of the animal.
In all these instances of animal cults examples of the tendency to make the divine animal anthropomorphic have been seen. We have now to consider some instances of the complete anthropomorphic process.
An old bear cult gave place to the cult of a bear goddess and probably of a god. At Berne--an old Celtic place-name meaning "bear"--was found a bronze group of a goddess holding a patera with fruit, and a bear approaching her as if to be fed. The inscription runs, Deae Artioni Licinia Sabinilla. A local bear-cult had once existed at Berne, and is still recalled in the presence of the famous bears there, but the divine bear had given place to a goddess whose name and symbol were ursine. From an old Celtic Artos, fem. Arta, "bear," were derived various divine names. Of these Dea Artio(n) means "bear goddess," and Artaios, equated with Mercury, is perhaps a bear god. Another bear goddess, Andarta, was honoured at Die (Drôme), the word perhaps meaning "strong bear"--And- being an augmentive. Numerous place-names derived from Artos perhaps witness to a widespread cult of the bear, and the word also occurs in Welsh, and Irish personal names--Arthmael, Arthbiu, and possibly Arthur, and the numerous Arts of Irish texts. Descent from the divine bear is also signified in names like Welsh Arthgen, Irish Artigan, from Artigenos, "son of the bear." Another Celtic name for "bear" was the Gaulish matu Irish math, found in Matugenos, "son of the bear," and in MacMahon, which is a corrupt form of Mac-math-ghamhain, "son of the bear's son," or "of the bear."
Similarly a cult of the stag seems to have given place to that of a god with stag's horns, represented on many bas-reliefs, and probably connected with the underworld. The stag, as a grain-eater, may have been regarded as the embodiment of the corn-spirit, and then associated with the under-earth region whence the corn sprang, by one of those inversions of thought so common in the stage of transition from animal gods to gods with animal symbols. The elk may have been worshipped in Ireland, and a three antlered stag is the subject of a story in the Fionn saga. Its third antler, like the third horn of bull or boar, may be a sign of divinity.
The horse had also been worshipped, but a goddess Epona (Gaul. epo-s, "horse"), protectress of horses and asses, took its place, and had a far-spread cult. She rides a horse or mare with its foal, or is seated among horses, or feeds horses. A representation of a mare suckling a foal--a design analogous to those in which Epona feeds foals--shows that her primitive equine nature had not been forgotten. The Gauls were horse-rearers, and Epona was the goddess of the craft; but, as in other cases, a cult of the horse must have preceded its domestication, and its flesh may not have been eaten, or, if so, only sacramentally. Finally, the divine horse became the anthropomorphic horse-goddess. Her images were placed in stables, and several inscriptions and statuettes have been found in such buildings or in cavalry barracks. The remains of the cult have been found in the Danube and Rhine valleys, in Eastern Gaul, and in Northern Italy, all Celtic regions, but it was carried everywhere by Roman cavalry recruited from the Celtic tribes.
Epona is associated with, and often has, the symbols of the Matres, and one inscription reads Eponabus, as if there were a group of goddesses called Epona. A goddess who promoted the fertility of mares would easily be associated with goddesses of fertility. Epona may also have been confused with a river-goddess conceived of as a spirited steed. Water-spirits took that shape, and the Matres were also river-goddesses.
A statuette of a horse, with a dedication to a god Rudiobus, otherwise unknown, may have been carried processionally, while a mule has a dedication to Segomo, equated elsewhere with Mars. A mule god Mullo, also equated with Mars, is mentioned on several inscriptions. The connection with Mars may have been found in the fact that the October horse was sacrificed to him for fertility, while the horse was probably associated with fertility among the Celts. The horse was sacrificed both by Celts and Teutons at the Midsummer festival, undoubtedly as a divine animal. Traces of the Celtic custom survive in local legends, and may be interpreted in the fuller light of the Teutonic accounts. In Ireland a man wearing a horse's head rushed through the fire, and was supposed to represent all cattle; in other words, he was a surrogate for them. The legend of Each Labra, a horse which lived in a mound and issued from it every Midsummer eve to give oracles for the coming year, is probably connected with the Midsummer sacrifice of the horse. Among the Teutons the horse was a divine sacrificial animal, and was also sacred to Freyr, the god of fertility, while in Teutonic survivals a horse's head was placed in the Midsummer fire. The horse was sporadically the representative of the corn-spirit, and at Rome the October horse was sacrificed in that capacity and for fertility. Among the Celts, the horse sacrificed at Midsummer may have represented the vegetation-spirit and benefited all domestic animals--the old rite surviving in an attenuated form, as described above.
Perhaps the goddess Damona was an animal divinity, if her name is derived from damatos, "sheep," cognate to Welsh dafad, "sheep," and Gaelic damh, "ox." Other divine animals, as has been seen, were associated with the waters, and the use of beasts and birds in divination doubtless points to their divine character. A cult of bird-gods may lurk behind the divine name Bran, "raven," and the reference to the magic birds of Rhiannon in the Triads.