The Codex Borgia or Codex Yoalli Ehēcatl is a Mesoamerican ritual and divinatory manuscript. It is generally believed to have been written before the Spanish conquest of Mexico, somewhere within what is now southern or western Puebla. The Codex Borgia is a member of, and gives its name to, the Borgia Group of manuscripts.
The codex is made of animal skins folded into 39 sheets. Each sheet is a square 27 cm by 27 cm (11x11 inches), for a total length of nearly 11 meters (35 feet). All but the end sheets are painted on both sides, providing 76 pages. The codex is read from right to left. Pages 29–46 are oriented perpendicular to the rest of the codex. The top of this section is the right side of page 29, and the scenes are read from top to bottom. So the reader must rotate the manuscript 90 degrees in order to view the codex correctly. The Codex Borgia is organized into a screen-fold. Single sheets of the hide are attached as a long strip and then folded back and forth. Images were painted on both sides and painted over with a white gesso. Stiffened leather are used as end pieces by gluing the first and last strips in order to create a cover. The edges of the pages are overlapped and glued together, making the sheet edges hardly visible under the white gesso finish. The gesso creates a stiff, smooth, white finished surface that preserves the images below.
The Codex Borgia features eighteen pages of an astronomical narrative that shows the yearlong alteration of the rainy and dry season.
The Codex Borgia is named after the Italian Cardinal Stefano Borgia, who owned it before it was acquired by the Vatican Library.
The Codex Borgia was brought to Europe, likely Italy, some time in the early Spanish Colonial period. It was discovered in 1805 by Alexander von Humboldt among the effects of Cardinal Stefano Borgia. The Codex Borgia is presently housed in the Apostolic Library, the Vatican, and has been digitally scanned and made available to the public.
The first eight pages list the 260 day signs of the tonalpohualli (day sign), each trecena of 13 signs forming a horizontal row spanning two pages. Certain days are marked with a footprint symbol. Divinatory symbols are placed above and below the day signs.