It must be borne in mind, however, that all parts of the Celtic world were not equally affected by the material development in question.

Part of the complexity of the history of Celtic religion arises from the fact that we cannot be always certain of the degree of progress in civilisation which any given district had made, of the ideas which pervaded it, or of the absorbing interests of its life.

Another difficulty, too, is that the accounts of Celtic religion given by ancient authorities do not always harmonise with the indisputable evidence of inscriptions.

The probability is that the religious practices of the Celtic world were no more homogeneous than its general civilisation, and that the ancient authorities are substantially true in their statements about certain districts, certain periods, or certain sections of society, while the inscriptions, springing as they do from the influence of the Gallo-Roman civilisation, especially of Eastern Gaul and military Britain, give us most valuable supplementary evidence for districts and environments of a different kind.

The inscriptions, especially by the names of deities which they reveal, have afforded most valuable clues to the history of Celtic religion, even in stages of civilisation earlier than those to which they themselves belong.