section_path: History/Central Mexico in the classic and postclassic
section_name: Central Mexico in the classic and postclassic
paragraph_text: Central Mexico in the classic and postclassic
  
  It is a matter of debate whether the enormous city of Teotihuacan was inhabited by speakers of Nahuatl, or whether Nahuas had not yet arrived in central Mexico in the classic period. It is generally agreed that the Nahua peoples were not indigenous to the highlands of central Mexico, but that they gradually migrated into the region from somewhere in northwestern Mexico. At the fall of Teotihuacan in the 6th century CE, some city-states rose to power in central Mexico, some of them, including Cholula and Xochicalco, probably inhabited by Nahuatl speakers. One study has suggested that Nahuas originally inhabited the Bajío area around Guanajuato which reached a population peak in the 6th century, after which the population quickly diminished during a subsequent dry period. This depopulation of the Bajío coincided with an incursion of new populations into the Valley of Mexico, which suggests that this marks the influx of Nahuatl speakers into the region. These people populated central Mexico, dislocating speakers of Oto-Manguean languages as they spread their political influence south. As the former nomadic hunter-gatherer peoples mixed with the complex civilizations of Mesoamerica, adopting religious and cultural practices, the foundation for later Aztec culture was laid. After 900 CE, during the postclassic period, many sites almost certainly inhabited by Nahuatl speakers became powerful. Among them are the site of Tula, Hidalgo, and also city-states such as Tenayuca, and Colhuacan in the valley of Mexico and Cuauhnahuac in Morelos.