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 bark paper codices; from eyewitness accounts by Spanish conquistadors such as Hernán 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 Florentine Codex compiled by the Franciscan monk Bernardino de Sahagún with the help of indigenous Aztec informants. From the 13th century, the Valley of Mexico was the heart of Aztec civilization: here the capital of the Aztec Triple Alliance, the city of Tenochtitlan, was built upon raised islets in Lake Texcoco. The Triple Alliance formed a tributary empire expanding its political hegemony far beyond the Valley of Mexico, conquering other city states throughout Mesoamerica. At its pinnacle, Aztec culture had rich and complex mythological and religious traditions, as well as achieving remarkable architectural and artistic accomplishments. In 1521 Hernán Cortés, along with a large number of Nahuatl speaking indigenous allies, conquered Tenochtitlan and defeated the Aztec Triple Alliance under the leadership of Hueyi Tlatoani Moctezuma II. Subsequently, the Spanish founded the new settlement of Mexico City on the site of the ruined Aztec capital, from where they proceeded with the process of colonizing Central America.