The game of Nine Mens Morris is played on a board consisting of three concentric squares connected by lines from the middle of each of the inner square’s sides to the middle of the corresponding outer square’s side. Pieces are played on the corner points and on the points where lines intersect so there are 24 playable points. In Britain the game was typically played with 9 black pieces and 9 white pieces usually in the form of round counters. The colours are irrelevant as long as there are two different colours. The counters can be any shape and of any material just as long as there are 18 all together and that they all fit on the board.
The basic aim of Nine Mens Morris is to make “mills” – vertical or horizontal lines of three in a row. Every time this is achieved, an opponent’s piece is removed, the overall objective being to reduce the number of opponent’s pieces to less than three or to render the opponent unable to play. An opponent’s piece is removed by the player forming a Mill. To begin with the board is empty.
No dice is required for this game. Player’s toss a coin to decide who will play white – white moves first and has a slight advantage as a result. Play is in two phases. To begin with, players take turns to play a piece of their own colour on any unoccupied point until all eighteen pieces have been played. After that, play continues alternately but each turn consists of a player moving one piece along a line to an adjacent point.
During both of these phases, whenever a player achieves a mill, that player immediately removes from the board one piece belonging to the opponent that does not form part of a mill. If all the opponents pieces form mills then an exception is made and the player is allowed to remove any piece. It is only upon the formation of a mill that a piece is captured but a player will often break a mill by moving a piece out of it and then, in a subsequent turn, play the piece back again, thus forming a new mill and capturing another piece.
Captured pieces are never replayed onto the board and remain captured for the remainder of the game. The game is finished when a player loses either by being reduced to two pieces or by being unable to move.
Sometimes a “wild” rule is played for when a player is reduced to only three pieces. In this case, any player with only three pieces remaining is allowed to move from any point to any other point on the board regardless of lines or whether the destination point is adjacent.
Alternative Nine Men’s Morris board layouts have been used over the centuries. One common pattern adds four extra diagonal lines to the basic board outlined above, the lines being drawn from the corners of the inner square to the corners of the outer square. Pieces can be moved and mills made along these extra lines in the usual way. Two printable versions are with this pdf alone with printable counters.