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.