The Sign That Ended a Migration

Colonial-era Nahua accounts, including the pictorial Codex Mendoza and the oral histories recorded by Sahagun and Duran, describe the Mexica arriving at Lake Texcoco as the last stage of a long migration from a legendary homeland called Aztlan, guided along the way by the counsel and omens of their patron god Huitzilopochtli. On a marshy, largely undesirable island near the lake's western shore, already ringed by longer-established and more powerful city-states, the Mexica are said to have seen an eagle perched on a nopal cactus, in some tellings grasping a serpent, the specific sign Huitzilopochtli had promised would mark the end of their wandering and the location of their future capital.

Tenochtitlan's foundation on this unpromising, marginal site in 1325 CE was itself remembered as proof of divine rather than merely practical selection, since the Mexica held none of the political standing that would otherwise have secured them better land, and the lake's waters, canals and chinampa agricultural islands became inseparable from the city's identity and its later imperial rise.