Aztec Tōnalpōhualli (阿茲特克聖曆)

The 260-Day Sacred Count of the Mexica

Overview

The Tōnalpōhualli ('count of days/destinies') is the 260-day sacred calendar of the Aztec (Mexica) world — the same 260-day machine the Maya knew as the Tzolkʼin, with different sign-names. It interlocks two cycles: 20 named day-signs (tōnalli), from Cipactli (Crocodile) to Xōchitl (Flower), and the numbers 1 through 13. Their least common multiple, 20 × 13 = 260, is the length of the round. The 260 days also partition into 20 trecenas of 13 days each, and a continuous nine-day cycle of the Lords of the Night (Yohualtēuctin) runs beneath the count. A person's day-name — for example 9 Malīnalli — was their tōnalli, read by the day-keepers as their destiny.

Origin & history

The 260-day count is the oldest and most widespread calendar of Mesoamerica, shared across the Maya, Zapotec, Mixtec, and Aztec worlds for over two millennia. For the Mexica it governed the sacred year: birth-names, the fates of the newborn, the fortunes of days, and the great festival cycle were read from it. The classic correlation to the Western calendar is Alfonso Caso's, fixed to the fall of Tenochtitlan on 13 August 1521 (Julian), which fell on the day 1-Cōātl (Ce Cōātl) — set out in his 'Los calendarios prehispánicos' (UNAM, 1967).

Knowledge of the tōnalpōhualli survives in the great divinatory manuscripts — the tōnalāmatl, 'book of days' — recorded both before and after the conquest. The Codex Borbonicus, an early-colonial screenfold almost certainly copied from a pre-conquest original, opens with a complete 260-day tōnalāmatl, each trecena presided over by its deities. The day-keepers (tōnalpouhqui) were the specialists who read these books to name children and counsel on auspicious days. The cycle's mechanics are anchored to the Goodman–Martínez–Thompson (GMT) correlation constant 584283 — Julian Day 584283 = the Maya 4 Ahau = 4 Xōchitl — so the Aztec and Maya counts run in exact lockstep (1 Imix = 1 Cipactli).

How it works

askTIAN converts a Gregorian birth date to its Julian Day Number and applies the GMT-584283 day count — the identical correlation used by this repo's Maya Tzolkʼin engine — to derive three interlocking values: the day-number (1–13), the day-sign index (0–19, 0 = Cipactli), and the position 1–260 within the round (1 = 1 Cipactli). From these it returns the day-name signature (e.g. 9 Malīnalli), the day-sign in Nahuatl with its English gloss, the trecena (the 13-day wave the day opens within, named for its leading sign), and the presiding Lord of the Night from the continuous nine-day cycle (anchored so that 1 Cipactli falls under the first Lord, Xiuhtēuctli). The count is verified against the published converter at azteccalendar.com.

Good for

• Finding a birth date's Aztec day-name signature
• Day-sign (tōnalli) and day-number readings
• Trecena (13-day wave) and Lord-of-the-Night context
• Comparing the Aztec count with the Maya Tzolkʼin
• Mesoamerican calendrical and mythological content
• Choosing or interpreting auspicious days

Use cases

Birth Day-Name

Enter a birth date to receive its tōnalpōhualli signature — the day-sign (one of 20 tōnalli, Nahuatl plus English gloss) carried on its number (1–13), such as 9 Malīnalli, together with its position 1–260 in the sacred round.

Trecena & Lord of the Night

The response identifies the trecena (the 13-day period the day opens within, named for its leading day-sign) and the presiding Lord of the Night (Yohualtēuctli) from the continuous nine-day cycle — the layers the day-keepers used for finer reading.

Maya–Aztec Cross-Reference

Because the engine uses the same GMT-584283 correlation as the Maya Tzolkʼin (1 Imix = 1 Cipactli), an application can show the same calendar day under both traditions side by side.

Auspicious-Day Guidance

Day-keepers read the tōnalpōhualli to judge which days favoured which acts; an application can surface a date's day-sign, number, trecena, and night-lord as the basis for a reflective auspicious-day reading.

Key terms

Tōnalpōhualli

The 260-day Aztec sacred count, interlocking 20 day-signs with the numbers 1–13; the Mexica twin of the Maya Tzolkʼin.

Tōnalli (day-sign)

One of the 20 named day-signs, from Cipactli (Crocodile) to Xōchitl (Flower); combined with a number 1–13 it forms a person's day-name.

Trecena

A 13-day 'week' of the count; the 260 days fall into 20 trecenas, each named for the day-sign that opens it.

Lords of the Night (Yohualtēuctin)

A continuous cycle of nine deities — beginning with Xiuhtēuctli, the Turquoise/Fire Lord — that presides over the nights beneath the day count.

GMT-584283 correlation

The Goodman–Martínez–Thompson constant fixing the Mesoamerican day count to the Western calendar (Julian Day 584283 = 4 Ahau = 4 Xōchitl), keeping the Aztec and Maya counts in lockstep.

API

The askTIAN Aztec API converts a birth date into its tōnalpōhualli day-name signature using the GMT-584283 correlation (the Maya Tzolkʼin's twin, 1 Imix = 1 Cipactli), returning the day-sign, day-number, position in the 260-day round, trecena, and presiding Lord of the Night — verified against azteccalendar.com.

Endpoint: POST /trpc/aztec.tonalpohualli — 1 TIAN Points. See the API documentation and Playground.