Collapse of Teotihuacan

Teotihuacan, the largest city in the pre-Columbian Americas with an estimated population of 100,000 to 200,000 at its height, entered a period of steep decline and partial destruction beginning around 550 CE, with the process largely complete by around 650 CE. Archaeological evidence shows that the city's major ceremonial structures along the Avenue of the Dead, including sections of the Pyramid of the Sun and the Temple of Quetzalcoatl complex, were deliberately burned and their monuments defaced in an episode of internal violence, rather than destroyed by an identified external invading force, though the precise causes remain debated among archaeologists. Proposed explanations include internal social unrest and elite conflict, prolonged drought that undermined the agricultural base supporting the city's population, and disruption of the long-distance trade networks that had sustained Teotihuacan's economic dominance over central Mexico. The city's collapse left a significant power vacuum in the Basin of Mexico that later Mesoamerican states, including the Toltecs and eventually the Aztecs, would remember and mythologize, with the Aztecs regarding the ruined city's monuments as sacred, giving it the Nahuatl name by which it survives today.