Nine Men's Morris is a strategy board game for two players dating at least to the Roman Empire. The game is also known as Nine Man Morris, Mill, Mills, The Mill Game, Merels, Merrills, Merelles, Marelles, Morelles and Ninepenny Marl in English. The game has also been called Cowboy Checkers and is sometimes printed on the back of checkerboards. Nine Men's Morris is a solved game in which either player can force the game into a draw.
The board consists of a grid with twenty-four intersections or points. Each player has nine pieces, or "men", usually coloured black and white. Players try to form 'mills'—three of their own men lined horizontally or vertically—allowing a player to remove an opponent's man from the game. A player wins by reducing the opponent to two pieces (where he could no longer form mills and thus be unable to win), or by leaving him without a legal move.
The game proceeds in three phases:
1. Placing men on vacant points
2. Moving men to adjacent points
3. (optional phase) Moving men to any vacant point when the player has been reduced to three men
