Classical Nahuatl (also known as Aztec, and simply Nahuatl) is a term used to describe the variants of the Nahuatl language that were spoken in the Valley of Mexico — and central Mexico as a lingua franca — at the time of the 16th-century Spanish conquest of Mexico. During the subsequent centuries it was largely displaced by Spanish and evolved into some of the modern Nahuatl dialects in use today (other modern dialects descend more directly from other 16th-century variants.) Although classified as an extinct language, Classical Nahuatl has survived through a multitude of written sources transcribed by Nahuas and Spaniards in the Latin alphabet.
Classical Nahuatl is an Uto-Aztecan language of the Nahuan or Aztecan language. It belongs to the central dialects and is most closely related to the modern dialects of Nahuatl spoken in the valley of Mexico in colonial and modern times. It is probable that the Classical Nahuatl documented by 16th- and 17th-century written sources represents a particularly prestigious sociolect. That is to say, the variety of Nahuatl recorded in these documents is most likely to be more particularly representative of the speech of Aztec nobles (pipiltin),..... full article at Wikipedia
