The first of the twenty trecenas that structure the 260 day tonalpohualli opens on 1 Cipactli, the earth caiman, and stands under the patronage of Tonacatecuhtli, lord of sustenance, one half of the creator pair Sahagun places at the head of Mexica cosmology, paired there with Tonacacihuatl and dwelling in Omeyocan, the place of duality atop the thirteen heavens. Sahagun's fourth book reads the whole thirteen day week as fortunate, promising those born within it prosperity and honour provided they kept the fasts and ritual duties the opening sign demanded, a conditional blessing typical of the readers' craft, in which a good trecena still required the discipline that kept its promise active.
As the count's own beginning, the trecena carries weight beyond its individual augury: Cipactli is read across Mesoamerica as the primordial ground the world itself was built upon, so a week opening on that sign was understood as a beginning proper, favourable for whatever a person meant to see grow, a planting, a marriage, an apprenticeship. The tonalpouhque, the professional readers Sahagun describes consulting for every significant undertaking, opened their explanation of the whole 260 day cycle from this trecena, since Mexica reckoning always started the count here.