Aztec

Mexica tradition held that the people migrated from a homeland called Aztlan, of uncertain location, arriving in the Valley of Mexico as a comparatively late and initially marginal group among older established city-states. Founding legend places the building of Tenochtitlan in 1325 CE on a swampy island in Lake Texcoco, chosen after priests saw an eagle perched on a cactus, an omen still on Mexico's flag today. In 1428, Tenochtitlan joined Texcoco and Tlacopan in the Triple Alliance, which expanded rapidly through conquest and, more often, the threat of it, ruling less as a unified territorial empire than as an overlordship: conquered city-states kept their own rulers but paid heavy tribute in goods, labor and captives to the alliance, Tenochtitlan foremost among its members.

Hernan Cortes landed on the Gulf coast in 1519 and reached Tenochtitlan the same year, exploiting resentment among tributary city-states, above all Tlaxcala, to build a large indigenous coalition against Mexica rule. Smallpox, introduced with the Spanish and devastating to a population with no prior immunity, killed enormous numbers including the emperor Cuitlahuac during the siege that followed, and Tenochtitlan fell in 1521. Colonial Nueva Espana built Mexico City directly atop the ruined Mexica capital. Much of what is known of pre-conquest life comes from later Nahua scholarship undertaken with Spanish friars, above all the Franciscan Bernardino de Sahagun's Florentine Codex, compiled with Nahua informants and illustrators decades after the conquest. Nahuatl-speaking Nahua communities remain a major living Indigenous population in central Mexico today, distinct from the specifically Mexica imperial elite the word "Aztec" most narrowly names.

Mexica cosmology held that the world had already been created and destroyed four times, each a failed "sun" or age ended by catastrophe, with the present age, the Fifth Sun, sustained only by the sun's continued motion across the sky. Huitzilopochtli, patron god of Tenochtitlan and its war and solar cult, presided over the Templo Mayor jointly with Tlaloc, the rain god, in a single dual pyramid at the heart of the city; Quetzalcoatl, the feathered serpent, was associated with wind, learning and the priesthood; Tezcatlipoca, the smoking mirror, governed fate, night and sorcery; and Coatlicue, mother of Huitzilopochtli, embodied the earth as both life-giving and devouring. Ritual timing ran on two interlocking calendars, the two hundred sixty day Tonalpohualli used for divination and naming, and the three hundred sixty five day solar year, realigning once every fifty two years in a cycle the Aztec Sun Stone, now in Mexico City's Museo Nacional de Antropologia, is popularly but not entirely accurately read as depicting.

Human sacrifice at the Templo Mayor is archaeologically well attested, but its scale and purpose remain debated. Mexica religious texts frame it as a necessary debt of blood repaying the gods for sustaining the sun and the world; anthropologist Michael Harner proposed in 1977 that large-scale sacrifice also met a nutritional need in a protein-scarce environment, a claim Bernard Ortiz de Montellano and other scholars have argued the evidence does not support, favoring Aztec cosmology's own terms over an imported ecological explanation. Spanish conquest-era accounts, written to justify conquest, likely inflated victim counts, so modern estimates rest on a difficult combination of skeletal evidence, colonial testimony and the Mexica's own religious framing.