The Aztecs had at least two manifestations of the supernatural: tētl and tēixiptla. Tētl, which the Spaniards and European scholars routinely mistranslated as "god" or "demon," referred rather to an impersonal, mysterious force that permeated the world. Tēixiptla, by contrast, denoted the physical representations ("idols," statues, and figurines) of the tētl as well as the human cultic activity surrounding this physical representation.

The Aztec religious cosmology included the physical earth plane, where humans lived, the underworld (or land of the dead), and the realm of the sky. Due to the flexible imperial political structure, a large pantheon of gods was incorporated into the larger cultural religious traditions. The Aztecs also worshipped deities that were central to older Mesoamerican cultures, such as the Olmecs. Some of the most central deities that the Aztecs paid homage to included:

• Huitzilopochtli – The “left-handed hummingbird” god was the god of war and the sun and also the founder of Tenochtitlan.
• Quetzalcoatl – The feathered serpent god that represented the morning star, wind, and life.
• Tlaloc – The rain and storm god.
• Mixcoatl – The “cloud serpent” god that was incorporated into Aztec belief and represented war.
• Xipe Totec – The flayed god that was associated with fertility. This deity was also incorporated from cultures under the Aztec Triple Alliance umbrella.

Huitzilopochtli as depicted in the Codex Telleriano-Remensis

This depiction of the war and sun god shows him in all of his warrior and ritual garb.

Founding Myth of Tenochtitlan

Veneration of Huitzilopochtli, the personification of the sun and of war, was central to the religious, social, and political practices of the Mexica people. Huitzilopochtli attained this central position after the founding of Tenochtitlan and the formation of the Mexica city-state society in the 14th century. According to myth, Huitzilopochtli directed the wanderers to found a city on the site where they would see an eagle devouring a snake perched on a fruit-bearing nopal cactus. (It was said that Huitzilopochtli killed his nephew, Cópil, and threw his heart on the lake. Huitzilopochtli honoured Cópil by causing a cactus to grow over Cópil's heart.) This legendary vision is pictured on the coat of arms of Mexico.

Ritual and Sacrifice

Like all other Mesoamerican cultures, the Aztecs played a variant of the Mesoamerican ballgame, named "tlachtli" or "ollamaliztli" in Nahuatl. The game was played with a ball of solid rubber, called an olli. The players hit the ball with their hips, knees, and elbows, and had to pass the ball through a stone ring to automatically win. The practice of the ballgame carried religious and mythological meanings and also served as sport. Many times players of the game were captured during the famous Aztec flower wars with neighboring rivals. Losers of the game were often ritually sacrificed as an homage to the gods.

A depiction of human sacrifice in the Codex Magliabechiano

This Spanish rendering of human sacrifices reflects the outsider's view of these ritual traditions.

While human sacrifice was practiced throughout Mesoamerica, the Aztecs, if their own accounts are to be believed, brought this practice to an unprecedented level. For example, for the reconsecration of the Great Pyramid of Tenochtitlan in 1487, the Aztecs reported that they sacrificed 80,400 prisoners over the course of four days, reportedly by Ahuitzotl, the Great Speaker himself. This number, however, is not universally accepted. Accounts by the Tlaxcaltecas, the primary enemy of the Aztecs at the time of the Spanish Conquest, show that at least some of them considered it an honor to be sacrificed. In one legend, the warrior Tlahuicole was freed by the Aztecs but eventually returned of his own volition to die in ritual sacrifice. Tlaxcala also practiced the human sacrifice of captured Aztec citizens.

Everyone was affected by human sacrifice, and it should be considered in the context of the religious cosmology of the Aztec people. It was considered necessary in order for the world to continue and be reborn each new day. Death and ritual blood sacrifice ensured the sun would rise again and crops would continue to grow. Not only were captives and warriors sacrificed, but nobles would often practice ritual bloodletting during certain sacred days of the year. Every level of Aztec society was affected by the belief in the human responsibility to pay homage to the gods, and anyone could serve as a sacrificial offering.

Priests and Religious Architecture

A noble priest class played an integral role in the religious worship and sacrifices of Aztec society. They were responsible for collecting tributes and ensuring there were enough goods for sacrificial ceremonies. They also trained young men to impersonate various deities for an entire year before being sacrificed on a specific day.  These priests were respected by all of society and were also responsible for practicing ritual bloodletting on themselves at regular intervals. Priests could come from the noble or common classes, but they would receive their training at different schools and perform different functions.

Aztec pyramid of St. Cecilia Acatitlan

This pyramid is typical of Aztec religious architecture. Priests would have stood on the platform at the top to perform religious duties and sacrifices.

Priests performed rituals from special temples and religious houses. The temples were generally huge pyramidal structures that were covered over with a new surface every fifty-two years, meaning some pyramids were gigantic in scale. These feats of architectural display were the sites of large sacrificial offerings and festivals, where Spanish reports said blood would run down the steps of the pyramids. The priests often performed smaller daily rituals in small, dark temple houses where incense and images of important gods were displayed.

Aztec Calendar

Aztec sun calendar

This calendar shows the eighteen months circling around a representation of the sun.

The Aztecs based their calendar on the sun and utilized a 365-day religious calendar. It was split into eighteen twenty-day months, and each month had its own religious, and often agricultural, theme. For example, the late winter month Altcahualo fell between February 14 and March 5 and represented a time of sowing crops and fertility. The month Toxcatl occurred in May and was a time of drought in the central valley. The Aztecs saw this month as a time of renewal, and it involved a large festival where a young man that had been impersonating the god Tezcatlipoca for a full year would be sacrificed.