Most ethnic groups of central Mexico in the post-classic period shared basic cultural traits of Mesoamerica, and so many of the traits that characterize Aztec culture cannot be said to be exclusive to the Aztecs. For the same reason, the notion of "Aztec civilization" is best understood as a particular horizon of a general Mesoamerican civilization. The culture of central Mexico includes maize cultivation, the social division between nobility (pipiltin) and commoners (macehualtin), a pantheon (featuring Tezcatlipoca, Tlaloc, and Quetzalcoatl), and the calendric system of a xiuhpohualli of 365 days intercalated with a tonalpohualli of 260 days. Particular to the Mexica of Tenochtitlan was the patron God Huitzilopochtli, twin pyramids, and the ceramic ware known as Aztec I to IV.
From the 13th century, the Valley of Mexico was the heart of dense population and the rise of city-states. The Mexica were late-comers to the Valley of Mexico, and founded the city-state of Tenochtitlan on unpromising islets in Lake Texcoco, later becoming the dominant power of the Aztec Triple Alliance or Aztec Empire. It was an empire that expanded its political hegemony far beyond the Valley of Mexico, conquering other city states throughout Mesoamerica in the late post-classic period.
Aztec culture and history is primarily known through archaeological evidence found in excavations such as that of the renowned Templo Mayor in Mexico City; from indigenous writings; from eyewitness accounts by Spanish conquistadors such as Cortés and Bernal Díaz del Castillo; and especially from 16th- and 17th-century descriptions of Aztec culture and history written by Spanish clergymen and literate Aztecs in the Spanish or Nahuatl language, such as the famous illustrated, bilingual (Spanish and Nahuatl), twelve-volume Florentine Codex created by the Franciscan friar Bernardino de Sahagún, in collaboration with indigenous Aztec informants. Important for knowledge of post-conquest Nahuas was the training of indigenous scribes to write alphabetic texts in Nahuatl, mainly for local purposes under Spanish colonial rule. At its height, Aztec culture had rich and complex philosophical, mythological, and religious traditions, as well as achieving remarkable architectural and artistic accomplishments.