Can I take a piece that is part of a mill?

Normally no. Pieces inside a completed mill are protected. The one exception is when every one of your opponent's pieces is in a mill, and then you may take any of them.

What happens if I cannot move?

You lose. A player with no legal move loses immediately, even with plenty of pieces still on the board.

How many pieces do you need to keep playing?

Three. Once the placing phase is over, being reduced to two pieces loses the game, because two pieces can never form a mill.

Is Nine Men's Morris a solved game?

Yes. It was solved by retrograde analysis in 1993 and is a draw with perfect play from both sides. That has almost no bearing on human games, where mills are missed constantly.

How to play Nine Men's Morris

Nine Men's Morris is about as easy to learn as noughts and crosses and about as deep as draughts. Boards have been found cut into stone across the ancient world, and it was one of the most popular games in medieval Europe. Here is the whole thing.

The board

Three squares, one inside the next, joined by four lines running through the middle of each side. Pieces sit on the twenty-four intersections, not in the spaces. There is no point at the very centre. Each player has nine pieces.

The empty board: twenty-four points on three joined squares.

Phase one: placing

Players take turns putting one piece on any empty point. This lasts eighteen turns, nine each. Most beginners spend this phase building their own lines and lose because of it: placing is mostly about stopping your opponent, and about taking the four points where two lines cross, which are the busiest on the board.

Mills, and taking a piece

Three of your pieces along one marked line is a mill. The moment you close one, whether by placing or by moving, you remove one of your opponent's pieces from the board. It does not come back.

You may not take a piece that is part of one of their mills, unless every piece they have left is in a mill. Diagonals do not count, and three pieces that merely look like a row are not a mill unless the board actually draws a line through them.

Ivory has closed a mill along the top and may now remove any one dark piece.

Phase two: moving

Once all eighteen pieces are down, a turn means sliding one piece along a line to an adjacent empty point. You cannot jump, and you cannot move to a point that is not joined to the one you are on. If you break a mill and later move the piece back, it counts again and you take another piece.

The double mill

This is the tactic that wins games, and it is not the shape most people first draw. Two mills that share a piece are worth little: moving the shared piece breaks both at once, so leaving closes nothing and you take a piece only every second move, if the piece can move at all.

The shape you want is two mills that share no piece, each missing one point, with those two points next to each other. A single piece then shuttles between them and closes a mill on every single move. Five pieces are enough to build one, and an opponent who cannot block or break it is losing a piece a turn.

A running mill. The piece on d7 completes a7-d7-g7; sliding it to d6 completes b6-d6-f6, and sliding back completes this one again.

Phase three: flying

When a player is down to exactly three pieces, they may move to any empty point rather than only an adjacent one. It is a last-chance rule that keeps a losing side alive. Serious play often turns it off, because without it three pieces is usually lost.

How the game ends

Reduce your opponent to two pieces and the game is over: two pieces can never make a mill.
A player who has no legal move loses on the spot, however many pieces they have left.
If the same position occurs three times, or fifty moves pass with nothing taken, the game is drawn. Without these rules good players would never finish.

Where the game came from

Boards cut into stone have turned up in a great many places, including roofing slabs at the temple at Kurna in Egypt, though dating a scratch in a rock is guesswork and the usual claim of 1400 BC should be treated with care. What is certain is that the game was played across the Roman world, and that it became enormously popular in medieval Europe: boards are carved into cloister benches and cathedral seats across England, France and Germany, cut there by people who were supposed to be paying attention to something else.

The game was solved in 1993 by retrograde analysis: with perfect play from both sides it is a draw. That matters a great deal to computers and almost none to people, since a perfect game requires never once missing a mill, and nobody manages that.

Questions people ask

Can I take a piece that is part of a mill?: Normally no. Pieces inside a completed mill are protected. The one exception is when every one of your opponent's pieces is in a mill, and then you may take any of them.
Does breaking a mill and reforming it count again?: Yes. If you move a piece out of a mill and later move it back, the mill closes again and you take another piece. The decisive version is two mills that share no piece, each missing one point, with those two points adjacent: one piece then shuttles between them and closes a mill every move rather than every other one.
What happens if I cannot move?: You lose. A player with no legal move loses immediately, even with plenty of pieces still on the board.
How many pieces do you need to keep playing?: Three. Once the placing phase is over, being reduced to two pieces loses the game, because two pieces can never form a mill.
Is Nine Men's Morris a solved game?: Yes. It was solved by retrograde analysis in 1993 and is a draw with perfect play from both sides. That has almost no bearing on human games, where mills are missed constantly.

Play Nine Men's Morris online