Kevin HY Hau - Hello World 👋

📖 How to play Nine Men's Morris

One of the oldest board games still played: two players, a board of three squares inside each other, and nine stones each. Make rows of three (mills) to capture the other player's stones.

The three phases

• 1. Placing. White starts. Players take turns putting one stone on any empty point of the 24 points, until all 9 each are down.
• 2. Sliding. Now each turn you slide one of your stones along a line to a neighbouring empty point. No jumping.
• 3. Flying. If you are down to exactly 3 stones, you may fly: move any stone to any empty point. (You can turn this off in the Flying row.)

Mills and winning

• Three of your stones in a straight line (a side of a square, or a line across the middle) is a mill. When you close a mill, by placing or sliding, you remove one enemy stone.
• You may not take a stone that is inside an enemy mill, unless all the enemy's stones on the board are in mills.
• You win when the enemy has only 2 stones left (counting stones still in hand), or when the enemy cannot move.
• It is a draw if the same position comes up three times, or after 200 moves (a removal counts as a move) with no winner.

Tips

• Mobility beats greed in the placing phase. A stone on a crossing point (the middle of a side of the middle square has 4 neighbours) can go more places than one in a corner. Trying to make mills too early often leaves your stones stuck.
• Block as you build. If the enemy has two in a row with the third point empty, put a stone there (or be ready to take a stone from the row).
• The running mill: slide a stone out of a mill and back in, again and again. Every time it closes you take a stone. A double mill (one stone that swings between two mills) is the deadliest shape.
• Blocking the enemy so they have no move is a win. Count their free neighbours before you spread out.
• 💡 Hint suggests a move (the computer thinks about 6 moves ahead). ↩ Undo takes back your last turn and the computer's reply.

Where it comes from

• Boards like this are scratched into stone in many parts of the world, and the game was played across Europe for hundreds of years, which is why it has many names (Mill, Merels, Morabaraba, Cowboy checkers). Nobody can say exactly how old it is.
• It is a solved game: in 1993-96 Ralph Gasser's computer search showed that with perfect play from both sides it is a draw. So the winner is the player who makes the first mistake.
• This page uses the standard rules above. Some families play a few details differently (for example, whether flying exists or whether you can remove from a mill), so check the rules in your house.

The computer is a plain look-ahead search (it tries moves, then the replies, then the replies to those, as deep as time allows) with a hand-made score for stones, mills and freedom to move. Master looks about 8 moves ahead on a fast machine. It is not a perfect player.