The evolution of a higher cultus is frequently identified with a more intimate acquaintance with the heavenly bodies, but it is not generally appreciated or understood by students of Comparative Religion that at least two different kinds of conception underlie the general idea. A luminary, sun, moon, or star, may be deified and achieve godhead by reason of striking natural characteristics, or, on the other hand, it may be identified with some god already known. Thus Mexican myth, as related to Sahagun by the natives, asserted that the gods met at Teotihuacan and told how two of their number, Nanahuatl and Tecciztecatl, sacrificed themselves by leaping into a great fire, becoming the sun and moon respectively. The remaining gods, sacrificing themselves also, “conferred life upon the stars,” that is they became identified with the several stellar constellations, becoming known as the Centzon Mimixcoa and Centzon Uitznaua, or “Four hundred Northerners” and “Four hundred Southerners,” as they occupied the sky on its northern or southern side. [23] Although this myth and a version of it current at Texcuco and given by Mendieta in his Historia Ecclesiastica [24] both represent Nanahuatl as the sun-god, he was not so known in Mexican popular religion and priestly practice, and was indeed a form of the god Xolotl, a deity of obscure characteristics. Tecciztecatl certainly was regarded as the moon-god, but the solar luminary was known as Tonatiuh or Piltzintecutli. As has already been stated, there are sound reasons for the belief that the solar cult was a relatively late institution in Mexico, although in some parts of the country it may have flourished for generations before it became popular in Tenochtitlan. Slightly elaborating our former reasons for this statement, we may indicate: (1) The name Tonatiuh appears in the myths of the origin of the sun as that of the luminary, but not of a god. (2) The circumstance that Tonatiuh was regarded by the Mexicans as a “heaven,” a Valhalla, to which the warriors slain in sacrifice betook themselves after death, and therefore represented a place of reward, a class of myth which is nearly always of comparatively late origin, and is the fruit of mature speculation. (3) The fact that Tonatiuh was closely identified with the warrior caste and therefore with human sacrifice, which was a late introduction and the paramount reason for the existence of that caste. (4) That the original Calendar was a lunar one. But these and other considerations will be dealt with more fully when we undertake the elucidation of the sun-god’s characteristics.