Aztec drought rituals, 16th century. Illustration of priests with jade necklaces performing rituals and casting decapitated birds into a stream to ward against drought. One carries a staff and a copal incense burner, another blows a conch shell, and the third is killing a bird. The flowering cactus (upper right) represents Tenochtitlan (Mexico City). 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.