This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
A veintena entry records one of the eighteen twenty day periods that made up the Aztec solar year, the xiuhpohualli, each carrying its own named feast, its own patron deity or deities, and its own documented rites, as recorded by Bernardino de Sahagun's Nahua informants in the Florentine Codex.
An entry records a veintena's documented position within the eighteen period year, the deity or deities its feast honored, and the specific rites the Codex describes for it, since the eighteen periods were not identical in character but each carried its own distinct observance tied to the agricultural or ritual concerns of its season.
The Florentine Codex is an indispensable and irreplaceable record of this material, and also not neutral testimony: it was compiled from Nahua informants working under Franciscan direction, describing practices those same authorities were actively working to suppress, so an entry cites it as evidence of what was reported under those conditions, honestly, rather than as an unmediated pre conquest voice. An entry also records, where the Codex provides it, the specific offerings, performers or ritual objects a feast involved, since Sahagun's informants described these particulars in enough documented detail to distinguish one veintena's observance from another's.