the Olmec civilization, which emerged around 2000 BCE during the Early Preclassic. It is documented that around this time many Mesoamerican languages adopted loanwords from the Mixe–Zoquean languages, particularly loanwords related to such culturally fundamental concepts as agriculture and religion. This has led some linguists to believe that the carriers of Olmec culture spoke a Mixe–Zoquean language and that words spread from their language into others because of their potential cultural dominance in the Preclassic period, though the relationship between the Olmec and other Preclassic groups is still debated (see Olmec influences on Mesoamerican cultures). During this time the Oto-Manguean languages diversified and spread into Oaxaca and central Mexico. In the Valley of Oaxaca, the Oto-Manguean Zapotec culture emerges around c. 1000 BCE. The splitting of Proto-Mayan into the modern Mayan languages slowly began at roughly 2000 BCE when the speakers of Huastec moved north into the Mexican Gulf Coast region. Uto-Aztecan languages were still outside of Mesoamerica during the Preclassic, their speakers living as semi-nomadic hunter-gatherers on the northern rim of the region and co-existing with speakers of Coracholan and Oto-Pamean languages. Classic period (200–1000 CE) During the Classic period the linguistic situation simultaneously becomes both clearer and more obscure. While the Maya actually left examples of their writing, researchers have been unable to determine the linguistic affiliations of several important Classic civilizations, including Teotihuacan, Xochicalco, Cacaxtla, and El Tajín. During this time it is well established that Mixtec languages were spoken at Tilantongo and Zapotec at Monte Albán (in the Valley of Oaxaca). The linguistic situation of the Maya area is relatively clear – Proto-Yucatec and Proto-Cholan were established in their respective locations in Yucatán and in the Tabasco area. Around 200 CE speakers of the Tzeltalan branch of Proto-Cholan moved south into Chiapas displacing speakers of Zoquean languages. Throughout the southern part of the Maya area and the highlands the elite of the Classic Maya centers spoke a common prestige language based on Cholan, a variant often referred to as Classic Ch'olti'an. An important question that remains to be answered is what language or languages were spoken by the people and rulers of the empire of Teotihuacan. During the first part of the Classic period Teotihuacan achieved dominance over central Mexico and far into the Maya area. Possible candidates for the language of Teotihuacan have been Nahuatl, Totonac or Mixe–Zoque. Terrence Kaufman has argued that Nahuatl is