After a century or so of slow decline, major civic-ceremonial structures in the city of Teotihuacan were burned and desecrated, probably around a.d. 600/650, at least some residential structures were abandoned, and the Teotihuacan state collapsed. Few features of Teotihuacan material culture survive in the Basin of Mexico in the ensuing Epiclassic period, which lasted from approximately a.d. 600/650-800/850. Ceramic and other lines of evidence suggest a sizable in-migration of peoples from western Mexico. These newcomers may have arrived in time to add to internal stresses responsible for bringing about Teotihuacan's collapse, arrived later to take advantage of that collapse, or both. Whatever the case, interactions with Teotihuacan survivors were complex and still poorly understood. Descendants of Teotihuacanos probably soon adopted new cultural identities, making them untraceable in the archaeological record, except possibly by biological markers.