A language which was the ancestor of Pochutec split from Proto-Nahuan (or Proto-Aztecan) possibly as early as AD 400, arriving in Mesoamerica a few centuries earlier than the bulk of speakers of Nahuan languages. Some Nahuan groups migrated south along the Central American isthmus, reaching as far as Nicaragua. The critically endangered Pipil language of El Salvador is the only living descendant of the variety of Nahuatl once spoken south of present-day Mexico. Beginning in the 7th century, Nahuan speakers rose to power in central Mexico. The people of the Toltec culture of Tula, which was active in central Mexico around the 10th century, are thought to have been Nahuatl speakers. By the 11th century, Nahuatl speakers were dominant in the Valley of Mexico and far beyond, with settlements including Azcapotzalco, Colhuacan and Cholula rising to prominence. Nahua migrations into the region from the north continued into the Postclassic period. One of the last of these migrations to arrive in the Valley of Mexico settled on an island in the Lake Texcoco and proceeded to subjugate the surrounding tribes. This group was the Mexica, who over the course of the next three centuries founded an empire named Tenochtitlan. Their political and linguistic influence came to extend into Central America and Nahuatl became a lingua franca among merchants and elites in Mesoamerica, e.g., among the Maya Kʼicheʼ people. As Tenochtitlan grew to become the largest urban center in Central America and one of the largest in the world at the time, it attracted speakers of Nahuatl from diverse areas giving birth to an urban form of Nahuatl with traits from many dialects. This urbanized variety of Tenochtitlan is what came to be known as Classical Nahuatl as documented in colonial times. Colonial period With the arrival of the Spanish in 1519, Nahuatl was displaced as the dominant regional language, but remained important in Nahua communities under Spanish rule. There is extensive colonial-era documentation in Nahuatl for Tlaxcala, Cuernavaca, Culhuacan, Coyoacan, Toluca and other locations in the Valley of Mexico and beyond. Starting in the 1970s, scholars of Mesoamerican ethnohistory have analyzed local-level texts in Nahuatl and other indigenous languages to gain insight into cultural change in the colonial era via linguistic changes, known at present as the New Philology. A number of these texts have been translated and published in part or in their entirety. The types of documentation include censuses,