A recent study of the Tonalámatl Aubin, an ancient Aztec divinatory manuscript, has confirmed its pre-Hispanic origin. Conducted by researchers from Mexico’s National Autonomous University (UNAM) and the National Institute of History and Anthropology (INAH), the study analyzed the codex, which was created at the end of the 15th century. The manuscript was made on a support crafted around 1424 from "amatl," a type of bark paper used by the Aztecs for writing, clothing, and rituals. Originally composed of 20 sheets, only two remain today, each measuring 24 by 27 centimeters and folded together to form a band. The Tonalámatl Aubin is more than a simple book—it is a calendar. The Nahuatl word "tonalli" means "day," and the codex contains the Aztec religious calendar, the Tonalpohualli, which consists of 260 days. Used for divination, the manuscript was read from top to bottom and right to left. Each page features deities associated with a 13-day cycle (called a trecena) at the top left, with smaller squares depicting gods linked to each individual day, enabling users to make daily predictions. It closely resembles the Codex Borbonicus, another Aztec calendar, though the two differ in reading direction. The Tonalámatl Aubin was radiocarbon dated and analyzed by experts from the National Library of Anthropology and History of Mexico and the University of Colorado at Boulder. Their findings suggest the manuscript was created after 1450, with a possible range of 30 to 40 years. The amatl bark used for the pages was made around 1424, placing the codex firmly in the precolonial period. This evidence supports its indigenous origin and confirms it was created before Spanish colonization. Today, the Tonalámatl Aubin is in Mexico after being stolen from the National Library of France in 1982 by a Mexican lawyer who successfully fought for its return. The manuscript’s history has raised questions about its origins, as it was hidden during the Spanish conquest. According to INAH, this period of concealment reflects the efforts of indigenous people to protect their pre-Hispanic beliefs under Spanish rule. The codex was first acquired in 1740 by a European in New Spain, passed through various hands, and eventually purchased in 1841 by Joseph Marius Alexis Aubin, a French collector whose collection later became part of the National Library of France.