Rithmomachia is a medieval board game, based on number theory. Pieces moves on a board, made of squares, have a shape, and a number, and players must try to get arrangements where the numbers of pieces in some group fulfill some mathematical property.
In the 16th century, Jean de Boissiere published the rules of this game. A translation of that text appeared in an article called Boissiere's Pythagorean Game by John F. C. Richards, Scripta Mathematica 12: 177-217, 1946.
Another (accurate) description of Rithmomachia can be found in an article by Michel Boutin in Jeux & Stratégie #26, April-May 1984.
In books of R. Bell, also a description of the game can be found, but unfortunately, Bell's description is rather inaccurate.
In 2001, a book on this game appeared, written by Ann E. Moyer from the Department of History, University of Pennsylvania, USA. The book discusses the game's role in medieval and Renaissance learning (including its close ties to chess), and features a complete edition of an Elizabethan game manual (in English), so that readers can construct a game set and play it.
Ann E. Moyer, The Philosophers’ Game: Rithmomachia in Medireview and Renaissance Europe, University of Michigan Press, September 2001. ISBN 0-472-11228-7