The Mexica told their own origin as a migration: a people sent from Aztlan by Huitzilopochtli, wandering until they saw the promised sign of an eagle on a cactus on an island in the lake, where they founded Tenochtitlan in 1325. A century later, after helping to overthrow the Tepanec overlords, they formed with Texcoco and Tlacopan the alliance that became the empire.
Their capital was built as a diagram. At its centre the Templo Mayor rose as a double pyramid carrying two shrines side by side, one to Tlaloc, who brought the rain, and one to Huitzilopochtli, who was the sun and the war god, so that the agricultural and the martial halves of the world stood on one platform. Eduardo Matos Moctezuma's excavations from 1978 found seven superimposed constructions, each enlargement burying the last, and more than a hundred deposited offerings containing objects brought from every corner of the tributary empire, which made the temple a map of what the empire had absorbed.
The system that governed it was the calendar: a 260 day ritual count and a 365 day year interlocking in a round of 52 years. At the end of each round every fire in the world was extinguished and a new one kindled on a hilltop at midnight, and Miguel Leon-Portilla's study of Nahua thought shows the philosophers of this culture arguing, in the poetry they called flower and song, about whether anything on earth is true or lasting.