found: Work cat.: Holl, A. Spiel mit Zahlen - Kampf mit Zahlen? : das mittelalterliche Zahlenkampfspiel Rithmomachie in seiner Regensburger Fassung um 1090, 2005.
found: Chessvariants WWW site, June 12, 2006:p. 1 (Rithmomachia is a medieval board game, based on number theory. Pieces move 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 fulfil some mathematical property.)
found: Gamecabinet WWW site, June 12, 2006:p. 1 (Rithmomachia - This complex chess-like game appeared in the western world around the year 1000. The game knew a great burst of popularity in the 15th century, because of some rule changes. When chess also saw its rules change ... Rithmomachia started fading rapidly, at the close of the 16th century.)
notfound: Shorter OED;Web. 3
