In dealing with the subject of ‘Celtic Religion’ the first duty of the writer is to explain the sense in which the term ‘Celtic’ will be used in this work. It will be used in reference to those countries and districts which, in historic times, have been at one time or other mainly of Celtic speech. It does not follow that all the races which spoke a form of the Celtic tongue, a tongue of the Indo-European family, were all of the same stock. Indeed, ethnological and archÆological evidence tends to establish clearly that, in Gaul and Britain, for example, man had lived for ages before the introduction of any variety of Aryan or Indo-European speech, and this was probably the case throughout the whole of Western and Southern Europe. Further, in the light of comparative philology, it has now become abundantly clear that the forms of Indo-European speech which we call Celtic are most closely related to those of the Italic family, of which family Latin is the best known representative. From this it follows that we are to look for the centre of dissemination of Aryan Celtic speech in some district of Europe that could have been the natural centre of dissemination also for the Italic languages. From this common centre, through conquest and the commercial intercourse which followed it, the tribes which spoke the various forms of Celtic and Italic speech spread into the districts occupied by them in historic times. The common centre of radiation for Celtic and Italic speech was probably in the districts of Noricum and Pannonia, the modern Carniola, Carinthia, etc., and the neighbouring parts of the Danube valley. The conquering Aryan-speaking Celts and Italians formed a military aristocracy, and their success in extending the range of their languages was largely due to their skill in arms, combined, in all probability, with a talent for administration. This military aristocracy was of kindred type to that which carried Aryan speech into India and Persia, Armenia and Greece, not to speak of the original speakers of the Teutonic and Slavonic tongues. In view of the necessity of discovering a centre, whence the Indo-European or Aryan languages in general could have radiated Eastwards, as well as Westwards, the tendency to-day is to regard these tongues as having been spoken originally in some district between the Carpathians and the Steppes, in the form of kindred dialects of a common speech. Some branches of the tribes which spoke these dialects penetrated into Central Europe, doubtless along the Danube, and, from the Danube valley, extended their conquests together with their various forms of Aryan speech into Southern and Western Europe. The proportion of conquerors to conquered was not uniform in all the countries where they held sway, so that the amount of Aryan blood in their resultant population varied greatly. In most cases, the families of the original conquerors, by their skill in the art of war and a certain instinct of government, succeeded in making their own tongues the dominant media of communication in the lands where they ruled, with the result that most of the languages of Europe to-day are of the Aryan or Indo-European type. It does not, however, follow necessarily from this that the early religious ideas or the artistic civilisation of countries now Aryan in speech, came necessarily from the conquerors rather than the conquered. In the last century it was long held that in countries of Aryan speech the essential features of their civilisation, their religious ideas, their social institutions, nay, more, their inhabitants themselves, were of Aryan origin.

A more critical investigation has, however, enabled us to distinguish clearly between the development of various factors of human life which in their evolution can follow and often have followed more or less independent lines. The physical history of race, for instance, forms a problem by itself and must be studied by anthropological and ethnological methods. Language, again, has often spread along lines other than those of race, and its investigation appertains to the sphere of the philologist. Material civilisation, too, has not of necessity followed the lines either of racial or of linguistic development, and the search for its ancient trade-routes may be safely left to the archÆologist. Similarly the spread of ideas in religion and thought is one which has advanced on lines of its own, and its investigation must be conducted by the methods and along the lines of the comparative study of religions.

In the wide sense, then, in which the word ‘Celtic religion’ will be used in this work, it will cover the modes of religious thought prevalent in the countries and districts, which, in course of time, were mainly characterised by their Celtic speech. To the sum-total of these religious ideas contributions have been made from many sources. It would be rash to affirm that the various streams of Aryan Celtic conquest made no contributions to the conceptions of life and of the world which the countries of their conquest came to hold (and the evidence of language points, indeed, to some such contributions), but their quota appears to be small compared with that of their predecessors; nor is this surprising, in view of the immense period during which the lands of their conquest had been previously occupied. Nothing is clearer than the marvellous persistence of traditional and immemorial modes of thought, even in the face of conquest and subjugation, and, whatever ideas on religion the Aryan conquerors of Celtic lands may have brought with them, they whose conquests were often only partial could not eradicate the inveterate beliefs of their predecessors, and the result in the end was doubtless some compromise, or else the victory of the earlier faith.

But the Aryan conquerors of Gaul and Italy themselves were not men who had advanced up the Danube in one generation. Those men of Aryan speech who poured into the Italian peninsula and into Gaul were doubtless in blood not unmixed with the older inhabitants of Central Europe, and had entered into the body of ideas which formed the religious beliefs of the men of the Danube valley. The common modifications of the Aryan tongue, by Italians and Celts alike, as compared with Greek, suggests contact with men of different speech. Among the names of Celtic gods, too, like those of other countries, we find roots that are apparently irreducible to any found in Indo-European speech, and we know not what pre-Aryan tongues may have contributed them. Scholars, to-day, are far more alive than they ever were before to the complexity of the contributory elements that have entered into the tissue of the ancient religions of mankind, and the more the relics of Celtic religion are investigated, the more complex do its contributory factors become. In the long ages before history there were unrecorded conquests and migrations innumerable, and ideas do not fail to spread because there is no historian to record them.

The more the scanty remnants of Celtic religion are examined, the clearer it becomes that many of its characteristic features had been evolved during the vast period of the ages of stone. During these millennia, men had evolved, concomitantly with their material civilisation, a kind of working philosophy of life, traces of which are found in every land where this form of civilisation has prevailed. Man’s religion can never be dissociated from his social experience, and the painful stages through which man reached the agricultural life, for example, have left their indelible impress on the mind of man in Western Europe, as they have in every land. We are thus compelled, from the indications which we have of Celtic religion, in the names of its deities, its rites, and its survivals in folk-lore and legend, to come to the conclusion, that its fundamental groundwork is a body of ideas, similar to those of other lands, which were the natural correlatives of the phases of experience through which man passed in his emergence into civilised life. To demonstrate and to illustrate these relations will be the aim of the following chapters.