An Aztec manuscript-calendar dating from the early 16th century (ca. 1507, although some scholars suggest it may have been created as late as 1540). The Codex Borbonicus consists of a long band of paper made from the bark of the amate tree. It is creased in the form of a folding screen and there are thirty-six different folios (rectangles made by folding the original), although originally the manuscript consisted of 40 different rectangles. The original was painted by Aztec High Priests using pigments from various plants, with red, green, tan and gray as the predominate colors.

Scholars believe that the primary function of the manuscript was to illustrate all of the elements of the Aztec cycle of 52 years as well as functioning as a yearly calendar. In each year, the Codex Borbonicus divides time into periods of thirteen days of which the calendar contains 20 series as well as establishing a larger series of 18 20 day months (totalling 360 days). The calendar not only made use of the solar year, but also tracked cycles of the moon. The calendar also fixed major religious and secular dates.

The Codex Borbonicus functioned not only as a practical calendar, but also as a book to determine horoscopes. Aztec religion contained numerous gods which governed every facet of natural and supernatural order. The deities governed developmental cycles in humans, plants and animals (including crops) and demanded propitiation by sacrifice and ceremonies to honor and recognize them at specific times determined by natural factors such as the junction of stars and planets. The Codex helped to codify the Aztec cycle of 52 years, as well as divine the future and give important information about dates neccessary for important religious (and secular) activities or ceremonies.

The original is being kept in the Bibliotheque de l'Assemblee Nationale in France and is possibly in the best condition of any Aztec Manuscript.

Information gleaned from numerous sources including: the Arizona State University Chicana and Chicano Art Resource, Encyclopaedia Britannica and Ancient Civilizations by Mahler, Johnson, et al