In discussing the religion and the social organisation of the Celtic peoples, I shall begin with religion. It is important to reflect, at the outset, that we must not think in terms of the great world religions, of our own Christian faith with its philosophy and theology and a highly developed ethical and moral doctrine of which the ideal of charity is the perfect expression. Nor even of Mohamedanism which owes so much to the Old Testament, nor of Hinduism or the nobler Buddhist form of Indian religion. We are dealing here with primitive magic, for which modern analogies would most readily be found in Africa or among the hill-tribes of India or the still pagan tribes of North America; though the general culture of the Celts of Gaul was higher than that statement implies, judged by their achievement in decorative art. They were heirs to common Indo-European traditions. Indeed an analogy can also be found with the cult of Poseidon and Demeter in Ancient Greece, as we shall see.
Our earliest information is about the Celts on the Continent, about the Gauls, for the Welsh and Irish sources date only from the Middle Ages. Caesar tells us that the Gauls were much given to religion, and he adds at they had a special devotion to Mercury as the entor of all the arts and crafts, and the patron of travellers and merchants, and that they also worshipped Apollo, Mars, Jupiter and Minerva. But he is simply equating Gaulish deities with his own Roman gods, as indeed the Romans equated some of their gods with the gods of the Greeks. He does not give us a single Gaulish name. Other Latin and Greek authors do give us names and many other names are found in inscriptions  dedicating monuments all over the vast area once dominated by the Celts, from Galatia in Asia Minor to Spain in the west.
We have more than four hundred names in all, and more than three hundred of them occur only once. It is evident that they are the names of local deities, each tribe or group of tribes having their special cult. Some of the names are worth mentioning here. The poet Lucan says that the three great gods of the Celts were Esus, Taranis and Teutates and each of these has a sort of echo in Irish tradition. The common Irish na Eogan means born of Esus”. Taranis sounds like th Irish word for thunder, torann . And Teutates seems to have been the title of the god of each tribe, not a proper name at all, for it is derived from the same root as the Irish word tuath tribe; and in Irish sagas, when a warrior takes an oath, he says, tongim do dia tonges mo thuath, I swear by the god by whom my people swear, that is to say, by Teutates, the tribal god, or so we may suppose.
Another name is important, that of the Irish Lug of the Long Arm. It occurs in Switzerland as a plural, Lugoues, and is common in the place-name Lugudunum which occurs in a great many places in Europe. It is the name of Lyons and London and Leon in France, Leiden in Holland and Liegnity in Silesia. This Lu must have been prominent among the gods of the Celts but we do not know what his special character was. He is the god of Lugnasad, the 1st of August, which was, I suppose, a harvest festival, and Lug may have been a god of fertility. Máire Mac Neill has recently shown, in a remarkable book, that the tradition of Lugnasad survived in the observance of Garland Sunday in many parts of Ireland until our own time. The sun and the moon, thunder and lightning, rain and fertility, birth and death, health and sickness, these were powers or concepts that a man had to conciliate, and we can be sure that they were all provided for, but, without written records, we  cannot tell whether any of the gods, whose names we know, was specially associated with one or other of them. Various guesses have been made. not without some foundation, but it would be tedious to discuss them here.
There is one element, the most important to a pagan, of which more can be said, namely the Earth herself, as a source of fertility. Many primitive peoples regarded the earth as a mother - we often speak of "mother earth - and the Celts worshipped her in triple form under the title matres or matrones . The dedications that survive on monuments in Gaul are in Latin, and the figures are sometimes represented with baskets of fruit or horns of plenty, or with children in their laps. They may have been goddesses of birth as well as of fertility, and this notion appears too in Irish and Welsh tradition. There is a Welsh place-name, Y Foel Famau, The Hill of the Mothers, and in Co. Kerry, The Paps are Dá Chích nAnann, which are mentioned in Cormacs glossary. Cormac says that Anu was the mother of the Gods and that she fed them well. She was then probably a goddess of birth and fertility.
Another feature of Celtic religion which emerges clearly is that wells, rivers, and sacred trees were objects of devotion and had patron gods or goddesses. Indeed, certain rivers seem to have been themselves divine. There was a sanctuary to the dea Sequana at the source of the river Seine and one to the dea Matrona near to the source of the Marne. In Ireland, the Boyne was a goddess and the mother of Oengus; and there were sacred trees in many places in Ireland. There is a special word, bile, for a sacred tree. And then there were animal-gods in Gaul, the bull, Taruos, and the mare, Epona, and the bear, Artos. In Ireland the bull-god survives in shadowy form in the great Táin, where the Brown Bull of Cualnge and the Whitehorned Bull seem to be supernatural beings, though they have lost a good deal of their sacred character in the telling of the saga.
The priests who maintained the cult of these gods were  the druids, and Caesar tells us a good deal about them They conducted the private and public sacrifices. They taught that the soul was immortal and passed after death into another body, rather as the Hindus believed. They also thought that all men were descended from the god of the Underworld, and they were learned in astronomy and natural history.
After a victory the captured animals were sacrifice to the god of war. At a private sacrifice or at the regular feasts of the year, the victim was perhaps a ram or bull or a bird, but we know little about Gaulish feasts or ritual, as the druids themselves have left no written records. Sometimes human victims were sacrificed, and, Caesar says that criminals were preferred, as being or pleasing to the gods, but that, failing them, even innocent victims were chosen.
We may turn to the Irish sources for more information and the sources here are plentiful, but they are very difficult to interpret because we have them only in sagas handed down by Christian monks. The wonder is that the good monks have told us so much.
ORahilly, in his great book on Early Irish History and Mythology, finds in Irish tradition a basic myth, the slaying of an Otherworld God, who is also the Sun-God by a Hero, and the god is slain with his own weapon. The Otherworld God is the Dagda or Eochaid Ollathair or Dian Cécht or Balor or Aed (a name which mean fire); and the hero is Lug, who slays Balor, or Cú Chulainn, who slays a dog-god, or Finn, who slays Gol, or Aed, or Cormac Mac Airt, whom ORahilly regard as an avatar of Lug, who, in one of his functions was the divine prototype of human kingship. The weapon is the thunderbolt or lightning, represented by a flashing sword, the Claidheamh Soluis of folklore. ORahilly may be right in these speculations, but he had not time to reduce them to order. Indeed, Gerard Murphy, in his important introduction to the third volume of Dunaire Finn, arrives at conclusions about Finn which support  ORahillys interpretation. But the myth that ORahilly here traces may not be Celtic at all and may lie in a deeper stratum of tradition. The legend of the Golden Bough, which Frazer chose as the title for his great work, is of a king killed with his own weapon, by the hero who succeeds him.
One observation of ORahillys is worth noting, because it has a bearing on what I said about the Gaulish gods. He says that the Otherworld God had many aspects or functions: he was a god of the Sun and of Thunder and Lightning and the ancestor of mankind. (Zeus, the god of the sky and father of men, is a Greek analogy.) And he points out that the tendency to departmentalise gods as gods of war, hunting, healing, fertility and so on, is partly the legacy of Greece, and not of general application. The Dagda (the Good God) of Irish tradition seems to have had various functions and may have had various names, Ollathair, Dian Cécht, Eochu and so on, to describe them.
I have now given you a good many Irish names and it is time to come closer to the Irish sources - to consider what we know about Irish, as distinct from Celtic, religion. The main dynasty of Irish gods was known as Tuatha Dé Danann, peoples of the Goddess Danu. Their chief was the Dagda, or Good God, whom we have already met, and who had other names as well. He was the lover of Boann, the river Boyne, and their son was Oengus. Other male gods were Lug and Midir and Nuadu of the Silver Arm and Cú Roé and Dond, who was god of the Underworld and sometimes thought of as the father of men. The array of goddesses is not very satisfying. Boann was one and there were Bé Find and Étain and Macha and Bodb, who was a raven-goddess associated with death. These gods were supposed to live in sacred mounds, really ancient burial-mounds of pre-Celtic times, as we now know. New Grange is one of these and it has recently been discovered that there, was another at Tara. Indeed, the whole of Meath is an  area of pre-Celtic grave-mounds, from the Lough Crew Hills to the Boyne Valley. But there were other gods who lived beyond the sea or under the sea. Manannán Mac Lir, Labraid Swift Hand on Sword and the goddess Fand, and who seem to belong to a separate tradition, and this tradition was common to Wales and Ireland for the Welsh Manawyddan fab Llyr is certainly Irish Manannán, though of course one may be simply a borrowing of the other.
The Tuatha Dé Danann were supposed to have defeated another group of supernatural beings called Fomuire or Fomorians, who may originally have defeated dwellers beyond or under the sea. But ORahilly regards them all as one, Balor, King of the Formorians, who was slain by Lug of the Tuatha Dé Danann, being simply one form of the Otherworld God. The truth is that scholars have not yet arrived at a clear understanding of Irish mythology, but there is plenty of material, as ORahilly shows.
Nothing is known about the religious practises of the ancient Irish, about sacrifices or forms of worship, a more than of the Gauls. There are, indeed, references to, human sacrifice in both areas and it may well that such gruesome rites took place in times of imminent disaster. There is an account of an idol, Crom Cruaic to which sacrifice was offered at Samain (November 1st) and we are told that St. Patrick destroyed the idol and forbade the rite. But it would seem to be a relic barbarism that has little to do with the gods we know about. Divination was practised by the druids of Gaul, who foretold the future by watching the flight of birds, by examining their entrails and so on. (The Roman augurs and soothsayers sought omens in similar ways.) And these practices were also common in Ireland have an interesting description of one such rite of divination in the saga of the Wasting Sickness of Chulainn. It is called tarbfeis, bull-feast, and is said have been a means of choosing a king. The saga is mere  legend, but the passage may preserve the tradition of a means of divination that was used:
This is how that bull-feast used to be made: to kill a white bull, and for one man to eat his fill of its flesh and of its broth, and to sleep after that meal, and for four druids to chant a spell of truth over him. And the form of the man to be made king used to be shown to him in a dream, his shape and his description, and the manner of work that he was doing. The man awoke out of his sleep, and told his dream to the king, a young warrior, noble and strong, with two red circles around his body, standing over the pillow of a sick man in Emain Macha.
There was doubtless a lot of this simple magic, and traces of it may be found in modern folklore. Human memory records various practices of the kind I have in mind, for instance, the sacrifice of a cock at the building of a new house, the placing of a live coal under the churn to ensure the coming of butter, and the knocking over of chairs when a corpse is leaving the house. These are, after all, propitiatory rites, but they hardly deserve to be called religion.
The Celts of Gaul and of Ireland certainly believed in an afterlife, that man survived in some sense after death, for they buried food containers and food and other provisions with their dead. Archaeology tells us that much. And the written sources tell us more. For Gaul we have the evidence of Julius Caesar, who says that the druids teach that souls do not die but pass from one to another after death: and this is confirmed by verses of the poet Lucan who says of the druids: From you we learn that the spirit animates the body in another world. If your songs are true, death is only the centre of a long life.
We have seen that the Irish believed in an Otherworld, sometimes called the Land of the Young or the Delightful Plain and imagined as somewhere on islands beyond the sea or under the sea. Some heroes are allowed to visit it during their lives, Bran and Conla and Cú  Chulainn and Oisín, and some never return. There is a poem in which Donn, the god of the dead, says All of you shall come to my house after your death. And perhaps DArbois and ORahilly are right in the opinion that the belief of the Celts was that after death they went to the house of their ancestor, the god of the Otherworld.
The gods were supernatural powers which you tried to get on your side or which you feared to offend. The French scholar, Fontenelle said long ago: For all divinities imagined by the pagans, the dominant idea is that of power, and they had little or no regard to wisdom or justice. They imagined their gods at a time when gods had nothing more precious to offer than power, and they imagined them in forms which bore the marks of power rather than of wisdom.
There were religious festivals in Ireland and we know something about them. There were four great feasts of the year. Imbolg (February 1st), Beltaine (May 1st), Lugnasad (August 1st) and Samain (November 1st). Of these Samain was the greatest and Beltaine the next. Samain was supposed to mean the end of summer, but, Vendryes suggests that it may be derived from sam, meaning one or together, which occurs in Latin semel and similis . At any rate it was a great feast, when the barrier between this world and the Otherworld was removed and contact with the gods was close. It was on this day that the feast of Tara was held, and Professor Binchy has made it probable that this was the inaugural feast of the King of Tara held only once in his reign and celebrating his ritual marriage with Sovereignty.
This is one ancient religious belief that we do grasp clearly, namely, that sovereignty ( flaithes ) was believed to be a puissance, a supernatural force, imagined as female, to which the king must be wedded, if his reign was to prosper. The ritual was even called banais rig, the kings wedding; it was the hieros gamos, or sacred marriage of Greek tradition and was, of course, a fertility rite. Giraldus Cambrensis reported an account he had heard of the inauguration of an Irish king, even after the Norman invasion, involving symbolic marriage with a mare, a rite which resembles the ancient horse-sacrifice of the Hindus and seems to be a survival, not merely of Celtic religion, but of ancient Indo-European tradition. We are reminded of the Greek cult of Poseidon and Demeter, who was mother earth; and they were honoured in the forms of horse and mare. The mating is of a god and goddess in Greece and of a king with a goddess in Ireland, but, there is a common element of mythology. Poseidon, too, by the way, had many names, Hippios, Melanthos, Asphaleios and so on; as god of horses and chariots, of earthquakes and the underworld, of the sea, and as father of men.
Of the other three feasts I have little to say. Of Imbolc we know little. In Christian times it was associated with the lambing seasion, but it may have been a time for ceremonies of purification like the Roman lustrations. Beltaine was May Day, the summer festival which is a day of celebration elsewhere than in Ireland, and Lugnasad had as patron the god Lug. We know that games and races were held on these festive occasions and the oenach or assembly was held then, too, when perhaps the king issued ordinances and arbitrated cases in dispute with the advice of a jurist.
There is one concept in Irish tradition which has to do with religion, or with magic, namely, the geis, which is an absolute prohibition from doing certain things. These gessa may be quite arbitrary and they vary with individuals. Sometimes they seem to be related,to the totem-cult, as when Cú Chulainn (Culanns Hound) may not eat the flesh of a dog, or Diarmait, whose lifespan was united to that of a boar, may not join in a boar-hunt, or Conaire, whose father was a bird, may not kill birds. Sometimes they appear to be motivated by the avoidance of a set of circumstances which had formerly led to disaster. In some cases a geis is imposed  by one man upon another, often by means of a successful exploit, as when Cú Chulainn lays a geis upon the Connachtmen, binding them not to pass the ford until a single warrior has removed the branch he has thrust into the ground. In some cases the geis seems to be quite accidental, a decree of fate. The basis of geis is honour. If a man violates his geis he loses honour, but violation of a geis involves also material ruin. The penalty is not stated, but in the sagas it is often death.
And then there was the practice of fasting as a means of redress, which is common to Ireland and to India. (It is not therefore specially Celtic, but rather an ancient Indo-European custom. Only the Celts preserved it in. this part of the world.) If a man had wronged you, you went to his house with witnesses, and remained there fasting - on hunger-strike - until you obtained redress of the wrong. This practice was fully recognised by law and indeed it plays an important part in the Brehon law tracts that survive.
We are passing from religion into the realm of social organisation, from the first to the second part of my subject. We know that there were kings in Ireland. In Gaul too there were once kings and the Gaulish word for king, rix, is common to personal names, Dumnorix, rí an domhain or king of the world, Vercingetorix, and the tribe of Bituriges kings of the world. But the era of kingship was passing when Caesar entered Gaul, and powerful tribes such as the Helvetii, the Aedui and the Arvetni were governed by an aristocracy without a king. Caesar tells us that in Gaul, society was divided into three classes, druides, equites and plebs, and this stratification of society is valid for Ireland ( fili, fáith, aithech ) and probably for Wales as well. He tells us that the druids underwent a very long period of training, twenty years, and that instruction was oral. The druids avoided the use of writing to preserve their tradition, for writing was an innovation unfit for recording sacred learning. They were teachers and judges as well as priests, instructing the  young men, settling private and public disputes, and practising divination by means of various rites. Like the brahmins in India, the druids were the highest class in society, and even kings could not make decisions without their approval, so that in truth it was they who gave orders, the kings being merely their servants and ministers of their will.
Besides the druids, there were two other classes of learned men, vates and bardi, prophets and bards. All of this is fully confirmed by the evidence of Irish sources. The long training - in Ireland it lasted for 12 years - the oral transmission of learning, and the exalted status of the druid. (We are told in the Táin that the king might not speak before the druid.) The Irish drui, fáith and bard, preserve the very same names. But in Christian Ireland the druids had been separated by function, and we find distinct professions of fili and brithem, the fili as poet, historian, genealogist and man of letters, the brithem as judge, and these two professions survived the coming of Christianity and continued to flourish, while the druid as pagan priest was, of course, doomed ta extinction.
Dr. Binchy has described Irish society as tribal, rural, hierarchical, and familiar, and his account may be taken as true of Celtic society in general. The tuath was a relatively small area, in Ireland the size of a modern barony though this must have varied in different counties with its king, himself subject to an over-king, the nobles, who were not land-owners, for the land belonged to the family, but who had wealth in cattle; and the commoners, who tilled the soil, paid food-rent to the king, and received cattle from the lord to graze the land. Then there were slaves, who had no rights.
The important unit was the family, a group consisting of the descendants of a common great-grandfather, four generations, and known in Ireland as the derbfine . This was the normal property-owning unit, and it was also the unit for the purpose of dynastic succession. Any  member of the kings derbfine was eligible to succeed him as king, his uncle or his brother or his nephew as well as his son. There was no legislature, no police, of course, no public administration of the law. But the old customary law was preserved, in memory, by the jurists and interpreted by them. If you refused to accept their decision, you were liable to be distrained upon by your neighbours and you had no remedy. Caesar tells us that in Gaul, persons who failed to comply with judicial decisions were excluded from the sacrifices and were deprived of honour and normal society. It was an ancient form of the boycott. And this was also true in Ireland.
There is one of Dr. Binchys terms that may not be of general application to Celtic society, the term rural. In ancient Ireland there were no towns, or even villages in the English sense. But on the continent there were defensible groups of dwellings, the Oppida, which offered resistance to the Roman advance. Ankara and Belgrade and Milan and Trier and Lyons are all old Celtic settlements, and they must have been fortified places in Celtic times.
And there is one other feature in which Gaul was ahead of Ireland and most of Britain, namely in the use of coinage, which they had learned from Greece and Rome.
The Celts were once a great and conquering people. They plundered Rome in the fourth century b.c., and Delphi in Greece in the third, spreading as far as Galatia in Asia Minor. The tide of fortune later turned against them and now the heirs to Celtic tradition survive only in Brittany and Wales and Scotland and Ireland. Like the Jews, it has been their destiny, for many centuries, to suffer wrongs rather than to inflict them. This is not an ignoble history, and the Celtic heritage is no mean tradition. It is a heritage of beauty in decorative art and in lyric poetry, of incandescent imagination in literature, of devotion to ideals rather than to material gain, of vitality and the will to survive, and indeed courage in battle too. "What was it that maintained you so in your lives? St. Patrick asks of Caoilte in the Colloquy of the Ancients, and Caoilte answered: Truth in our hearts, and strength in our arms, and fulfilment in our tongues.
This Celtic heritage is ours in a peculiar way, for we are the only independent people to possess it. We shall do well to cherish it.