Nahuatl (pronounced in two syllables, NA-watl ['na.watɬ]) is a term applied to some members of the Aztecan or Nahuan sub-branch of the Uto-Aztecan language family. The languages called "Nahuatl" are all Native American languages indigenous to central Mexico.
The term "Nahuatl" is often used specifically with reference to the Classical Nahuatl language, which was the language of the Aztec Empire, and, according to Aztec historiography, the earlier Toltec Empire, and was used as a lingua franca in much of Mesoamerica during the 7th century AD through the late 16th century, at which time its prominence and influence was interrupted by the Spanish conquest of the New World. It should be pointed out that Nahuatl influence increased slightly for some time before decreasing, as the Spaniards used Nahuatl to strengthen their influence over the conquered territories and to spread Christianity; it was even used in places it had not previously been spoken. This was also done (although not to the same extent) for the Quechua in South America. When the Spanish colonies began to gain independence, the Spanish-speaking leaders (mainly "criollos") made Spanish the predominant language.
The term "Nahuatl" also serves to identify a number of modern Nahuatl dialects (linguistic variants, some of them mutually unintelligible) that are still spoken by at least 1.5 million people in what is now Mexico, as well as small populations in El Salvador and the United States of America. All of these dialects show influence from the Spanish language to some degree, although the extent of this influence varies. No modern dialects are identical to Classical Nahuatl, but those spoken in and around the Valley of Mexico are generally more closely related to Classical Nahuatl than peripheral ones. Modern variants of Nahuatl are still the most widely spoken group of Native American languages in Mexico, although most Nahuatl speakers also speak Spanish as a second language.
Nahuatl was originally written with a pictographic script which was not a full writing system but instead served as a mnemonic to remind readers of texts they had learnt orally. The script appeared in inscriptions carved in stone and in picture books, many of which the Spanish destroyed. The Spanish introduced the Latin alphabet to write Nahuatl, and a large amount of prose and poetry was subsequently written. There has been considerable debate about how to spell Nahuatl in Latin script, as many of the sounds present in Nahuatl are not present in the Romance languages Latin was developed to express.