1 Calli

Trecena 15 opens on 1 Calli, house, under the patronage of Itzpapalotl, the obsidian butterfly, a fearsome goddess associated with the Tzitzimime, the star demons Mexica belief held would descend and devour humanity should the sun fail to rise, most feared during the darkness of a solar eclipse, and remembered in some sources as patroness of the Chichimec peoples of the northern deserts. Sahagun's fourth book gives this week's children sickness and misfortune, an augury the readers softened only by moving naming days to better numbers within the week, one of the more directly unfavourable trecenas in the whole count and matched to a patron whose own character carries little of the gentler ambiguity found in some of the pantheon's more forgiving deities.

A week for staying within walls and discharging duties owed, by the readers' own description, its house sign opening fits this reading of caution and enclosure directly: Calli, shelter and the hearth, read here not as safety freely enjoyed but as a confinement made necessary by the week's difficulty, a family kept close to home rather than venturing out under a dangerous sky. Calli is also one of the four year bearer signs, giving this trecena's opening additional weight whenever a solar year happened to begin on it.

Trecena 15 runs from 1 Calli through 13 Cuauhtli, eagle, its span carrying house, lizard, serpent, death, deer, rabbit, water, dog, monkey, grass and reed before closing on the sign that opens Trecena 19 next in the round. This trecena sits within the count's final third, and its difficult reading under Itzpapalotl's patronage places it among the small number of trecenas the tonalpouhque treated as calling for the most active remedial attention, the shifting of naming days and the addition of penance the sources describe as standard responses to a harsh augury rather than exceptional measures reserved only for this week.

The eagle sign that closes this trecena carries, elsewhere in the count, a reading of solar vigour and warrior standing under its own patron Xipe Totec, a markedly different character from the house sign's enclosure at this trecena's opening, so that a reader working through these thirteen days in order would have narrated a movement from confinement toward the eagle's eventual flight, even within a week whose overall augury the sources record as unfavourable. Boone's study of the surviving books of fate notes that difficult trecenas like this one were not omitted or softened in the painted codices, a directness the Mexica calendar priesthood treated as essential to the count's usefulness.