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.