De Matrica Bellae is a set of matrix game rules for tabletop wargames by Graham D. Evans and was published as the Society of Ancients incentive game for 2005. The matrix style of play often produces an anarchic type of game and also needs an umpire, but can produce an entertaining game that is good fun and can provide a lot of value to the wargamer. DMB also includes a bonus matrix game campaign, "Londinium's Burning" - a matrix version of the Iceni revolt led by Boudicca.

(from the SOA website)

Matrix games use structured arguments rather than mathematics to determine the success or failure of actions within the game.