Aztec blood sacrifices, 16th century. Illustration of two Aztec priests (tlamacazqui) with blue-coloured bodies and long hair making offerings to the gods. One holds an incense burner which is used to burn dried copal tree resin, while the other is cutting himself with a cactus spine. The cactus vessel at centre will house the blood offering. The Aztec Empire (ruled by the Mexica) was an alliance of three city states that ruled in central Mexico from 1428 until their defeat by Spanish conquistadors in 1521. Artwork from a 19th-century copy of a 16th-century post-conquest codex and history of the Aztecs by Jesuit missionary Juan de Tovar.