as they were considered mostly symbolic, representing formulas related to astronomical events, genealogy and historic events. Most surviving pre-Hispanic codices come from the late Mesoamerican period and early colonial period, as more of these escaped destruction over history. For this reason, more is known about the Aztec Empire than the Mayan cultures. Important Aztec codices include the Borgia Group of mainly religious works, some of which probably pre-date the conquest, the Codex Borbonicus, Codex Mendoza, and the late Florentine Codex, which is in a European style but executed by Mexican artists, probably drawing on earlier material that is now lost. Important museum collections in Mexico include those of the National Museum of Anthropology and the Museo Diego Rivera Anahuacalli, both in Mexico City, as well as provincial museums. Gallery Colonial era, 1521–1821 The early colonial era and criollo and indigenous artists and influences Since the Spanish conquest of the Aztec Empire, Mexican art has been an ongoing and complex interaction between the traditions of Europe and native perspectives. Church construction After the conquest, Spaniards' first efforts were directed at evangelization and the related task of building churches, which needed indigenous labor for basic construction, but they Nahuas elaborated stonework exteriors and decorated church interiors. Indigenous craftsmen were taught European motifs, designs and techniques, but very early work, called tequitqui (Nahuatl for "vassal"), includes elements such as flattened faces and high-stiff relief. The Spanish friars directing construction were not trained architects or engineers. They relied on indigenous stonemasons and sculptors to build churches and other Christian structures, often in the same places as temples and shrines of the traditional religion. "Although some Indians complained about the burden such labor represented, most communities considered a large and impressive church to be a reflection of their town's importance and took justifiable pride in creating a sacred place for divine worship." The fact that so many colonial-era churches have survived centuries it testament to their general good construction. The first monasteries built in and around Mexico City, such as the monasteries on the slopes of Popocatepetl, had Renaissance, Plateresque, Gothic or Moorish elements, or some combination. They were relatively undecorated, with building efforts going more towards high walls and fortress features to ward off attacks. The construction of more elaborate churches with large quantities of religious artwork would define much of the artistic output of the colonial period. Most of the production was related