The Aztec or Mexica calendar is the calendrical system used by the Aztecs as well as other Pre-Columbian peoples of central Mexico. It is one of the Mesoamerican calendars, sharing the basic structure of calendars from throughout the region.

The Aztec sun stone, also called the calendar stone, is on display at the National Museum of Anthropology in Mexico City. The calendar consists of a 365-day calendar cycle called xiuhpōhualli (year count), and a 260-day ritual cycle called tōnalpōhualli (day count). These two cycles together form a 52-year "century", sometimes called the "calendar round". The xiuhpōhualli is considered to be the agricultural calendar, since it is based on the sun, and the tōnalpōhualli is considered to be the sacred calendar.

The tōnalpōhualli ("day count") consists of a cycle of 260 days, each day signified by a combination of a number from 1 to 13, and one of the twenty day signs. With each new day, both the number and day sign would be incremented: 1. Crocodile is followed by 2. Wind, 3. House, 4. Lizard, and so forth up to 13. Reed. After Reed, the cycle of numbers would restart (though the twenty day signs had not yet been exhausted), resulting in 1. Jaguar, 2. Eagle, and so on, as the days immediately following 13. Reed. This cycle of number and day signs would continue similarly until the 20th week, which would start on 1. Rabbit, and end on 13. Flower. It would take a full 260 days (13×20) for the two cycles (of twenty day signs, and thirteen numbers) to realign and repeat the sequence back to 1. Crocodile.

Day signs

The set of day signs used in central Mexico is identical to that used by Mixtecs, and to a lesser degree similar to those of other Mesoamerican calendars. Each of the day signs bear an association with one of the four cardinal directions.^[1][2]

There is some variation in the way the day signs were drawn or carved. Those here were taken from the Codex Magliabechiano.

More information Image, Nahuatl name ...

Image Nahuatl name Pronunciation English translation Direction Cipactli [siˈpáktɬi] Crocodile Alligator Caiman Crocodilian Monster Dragon East Ehēcatl [eʔˈéːkatɬ] Wind North Calli [ˈkálːi] House West Cuetzpalin [kʷetsˈpálin̥] Lizard South Cōātl [ˈkóːwaːtɬ] Serpent Snake East Miquiztli [miˈkístɬi] Death North Mazātl [ˈmásaːtɬ] Deer Animal West Tōchtli [ˈtóːtʃtɬi] Rabbit South Ātl [ˈaːtɬ] Water East Itzcuīntli [itsˈkʷíːn̥tɬi] Dog North

Image Nahuatl name Pronunciation English translation Direction Ozomahtli [osoˈmáʔtɬi] Monkey West Malīnalli [maliːˈnálːi] Grass South Ācatl [ˈáːkatɬ] Reed East Ocēlōtl [oːˈséːloːtɬ] Ocelot Jaguar North Cuāuhtli [ˈkʷáːʍtɬi] Eagle West Cōzcacuāuhtli [koːskaˈkʷáːʍtɬi] Vulture South Ōlīn [ˈoːliːn̥] Movement Quake Earthquake East Tecpatl [ˈtékpatɬ] Flint Flint Knife North Quiyahuitl [kiˈjáwitɬ] Rain West Xōchitl [ˈʃoːtʃitɬ] Flower South

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Wind and Rain are represented by images of their associated gods, Ehēcatl and Tlāloc respectively.

Other marks on the stone showed the current world, and the worlds before this one. Each world was called a sun, and each sun had its own species of inhabitants. The Aztecs believed that they were in the Fifth Sun, and like all of the suns before them, they would also eventually perish due to their own imperfections. Every 52 years was marked out due to the belief that 52 years was a life cycle and at the end of any given life cycle, the gods could take all they had, and destroy the world.

In ancient times the year was composed of eighteen months, and thus it was observed by the native people. Since their months were made of no more than twenty days, these were all the days contained in a month, because they were not guided by the moon but by the days; therefore, the year had eighteen months. The days of the year were counted twenty by twenty.

— Diego Durán

Xiuhpōhualli is the Aztec year (xihuitl) count (pōhualli). One year consists of 360 named days and 5 nameless (nēmontēmi). These 'extra' days are thought to be unlucky. The year was broken into 18 periods of twenty days each, sometimes compared to the Julian month. The Nahuatl word for moon is metztli but whatever name was used for these periods is unknown. Through Spanish usage, the 20-day period of the Aztec calendar has become commonly known as a veintena.

Each 20-day period started on Cipactli (Crocodile) for which a festival was held. The eighteen veintena are listed below. The dates are from early eyewitnesses; each wrote what they saw. Bernardino de Sahagún's date precedes the observations of Diego Durán by several decades and is before recent to the surrender. Both are shown to emphasize the fact that the beginning of the Native new year became non-uniform as a result of an absence of the unifying force of Tenochtitlan after the Mexica defeat.

Veintenas of the xiuhpōhualli

More information #, Glyph ...

#	Glyph	Name	Gregorian range		Presiding deities
			Durán	Sahagún
1		ātl cāhualo (“the water ceases”) cuahuitl ēhua (“the trees rise”)	Mar 01–Mar 20	Feb 02–Feb 21	Water gods
2		tlācaxīpēhualiztli (“flaying of men”)	Mar 21–Apr 09	Feb 22–Mar 13	Xipe Totec
3		tōzōztōntli (“lesser vigil”)	Apr 10–Apr 29	Mar 14–Apr 02	Tlaloc
4		huēyi tōzōztli (“greater vigil”)	Apr 30–May 19	Apr 03–Apr 22	Cinteotl
5		toxcatl (“dryness”)	May 20–Jun 08	Apr 23–May 12	Tezcatlipoca
6		etzalcualiztli (“eating of cooked maize and beans”)	Jun 09–Jun 28	May 13–Jun 01	Tlaloque
7		tēcuilhuitōntli (“lesser feast day”)	Jun 29–Jul 18	Jun 02–Jun 21	Huixtocihuatl
8		huēyi tēcuilhuitōntli (“greater feast day”)	Jul 19–Aug 07	Jun 22–Jul 11	Xilonen
9		tlaxōchimaco (“giving of flowers”) miccāilhuitōntli (“lesser feast day of the dead”)	Aug 08–Aug 27	Jul 12–Jul 31	Huitzilopochtli
10		xocotl huetzi (“the xocotl falls”) huēyi miccāilhuitl (“greater feast day of the dead”)	Aug 28–Sep 16	Aug 01–Aug 20	Xiuhtecuhtli
11		ochpaniztli (“sweeping”)	Sep 17–Oct 06	Aug 21–Sep 09	Teteo Innan
12		teōtlehco (“the gods arrive”)	Oct 07–Oct 26	Sep 10–Sep 29	All the gods
13		tepēilhuitl (“feast day of mountains”)	Oct 27–Nov 15	Sep 30–Oct 19	Mountains
14		quechōlli (“roseate spoonbill”)	Nov 16–Dec 05	Oct 20–Nov 8	Mixcoatl
15		panquetzaliztli (“raising of banners”)	Dec 06–Dec 25	Nov 09–Nov 28	Huitzilopochtli
16		ātemoztli (“descent of water”)	Dec 26–Jan 14	Nov 29–Dec 18	Rain gods
17		tititl (“tightening,” “contraction”)	Jan 15–Feb 03	Dec 19–Jan 07	Tonan
18		izcalli (“offshoot,” “bud”)	Feb 04–Feb 23	Jan 08–Jan 27	Xiuhtecuhtli
–		nēmontēmi (“they fill up in vain”); Not a veintena, 5-day complementary period	Feb 24–Feb 28	Jan 28–Feb 01	None

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The ancient Mexicans counted their years by means of four signs combined with thirteen numbers, thus obtaining periods of 52 years,^[3] which are commonly known as Xiuhmolpilli, a popular but incorrect generic name; the most correct Nahuatl word for this cycle is Xiuhnelpilli.^[4] The table with the current years:

For many centuries scholars had tried to reconstruct the Calendar. A widely accepted version was proposed by Professor Rafael Tena of the Instituto Nacional de Antropología e Historia,^[5] based on the studies of Sahagún and Alfonso Caso of the National Autonomous University of Mexico. His correlation argues that the first day of the Mexica year was February 13 of the old Julian calendar or February 23 of the current Gregorian calendar. Using the same count, it has been the date of the birth of Huitzilopochtli, the end of the year and a cycle or "Tie of the Years", and the New Fire Ceremony, day-sign 1 Tecpatl of the year 2 Acatl,^[6] corresponding to the date February 22. A correlation by independent researcher Ruben Ochoa interprets pre-Columbian codices, to reconstruct the calendar, while ignoring most primary colonial sources that contradict this idea, using a method that proposes to connect the year count to the vernal equinox and placing the first day of the year on the first day after the equinox.^[7]

In this regard, José Genaro Emiliano Medina Ramos, a senior native nahua philosopher from San Lucas Atzala in the state of Puebla, proposes a multidisciplinary calendar reconstruction in náhuatl (‘centro de Puebla’ variant) according with his own nahua cosmosvision;^[8] and relying precisely on Ochoa's smart correlation and on Tena's presuppositions as well. His proposal was translated to Spanish and English, and codified as an academic webpage in 2023.^[9]

• Maya calendar
• Mesoamerican calendars
• Aztec New Year
• Muisca calendar