Until the beginning of the present century most Americanists held that Mexican civilization and consequently Mexican religion were the outcome of but a few generations of native progress. It is true that the Nahua people had behind them a relatively brief history of national and tribal life, but modern research has shown that they were undoubtedly the heirs of a civilization having early foundations and of considerable achievement and complexity, the religious aspect of which had arrived at a high state of development. [4] Evidences of the archaic character of this faith are rapidly accumulating, but many years must yet be dedicated to the examination and comparison of the data concerning it before it is possible to speak with any degree of certainty regarding the causes which contributed to its formation and evolution. Although we must necessarily regard Mexican religion as having had a progressive history spread over many generations, we are at present almost ignorant of the gradual changes which accompanied its growth. An effort will be made to outline the probable nature of these mutations, but the endeavour will not receive any great measure of assistance from the abundant but chaotic and unclassified material amassed by Americanists during the last twenty years, which in its present condition is not of much value as regards this particular branch of the subject, but which it is the writer’s intention to employ, so far as it is capable of illustrating the question before us. THE LITERATURE OF MEXICAN RELIGION It is necessary at this stage to deal briefly with the sources of Mexican religious history. A literature, bewildering in its scope and variety, has grown up around the subject of Mexican antiquity as a whole, and it is perhaps well for the student if he approaches it with only a partial realization of the spacious character of the material he must review. I have thought it best in such a work as this to relegate most of the bibliographical matter to an appendix, where an endeavour has been made to supply the student with a trustworthy catalogue of such manuscripts and works as are essential to the study of Mexican religion. It is hoped that this may prove of guidance and assistance and spare much initial toil. But for the present I will confine my remarks to such general observations upon the sources from which we partly glean our knowledge of the ancient Mexican faith as will serve the immediate purpose. These sources are four in number: (I) The native codices or paintings; (II) the native annals; (III) native art-forms in architecture, sculpture, pottery, and mural painting, depicting gods and other divine beings; and (IV) the writings of the Spanish conquerors of Mexico.