thumb|1554 illustration of a Rithmomachy board and pieces by Claude de Boissière
Rithmomachia (also known as rithmomachy, arithmomachia, rythmomachy, rhythmomachy, the philosophers' game, and other variants) is an early European mathematical board game. Its earliest known description dates from the eleventh century. The name comes loosely from Greek and means "The Battle of the Numbers."