Nine Men's Morris — free online board game vs computer

Nine Men's Morris is one of the oldest board games still played, cut into stone slabs long before anyone wrote its rules down. Both sides have nine pieces. You place them one at a time on the twenty-four points, then slide them along the lines to any empty neighbour. Line three of your own up on a line and you have a mill: take one of the opponent's pieces off the board, though never one that is itself in a mill unless every piece they have left is.

Lose your pieces down to three and the rules change in your favour — you may fly, jumping to any empty point on the board, which turns a lost position into a real fight. A side reduced to two pieces, or with no legal move left, has lost. There is one house rule on top: if thirty moves go by with nothing taken, the game is settled on pieces. Without it Morris does not end — measured, two engines shuffled past three hundred moves with four pieces each and nothing decided. Your score is wins in a row, the computer searches deeper with every one, and a draw ends the run the way a loss does.

How to play

• Placing: tap any empty point to put a piece down. Nine each, alternating.
• Moving: tap one of your pieces, then tap an empty point joined to it by a line.
• Mills: three of yours in a line lets you take one of theirs — tap the piece to remove.
• A piece in a mill is safe unless all of their pieces are in mills.
• Flying: once you are down to three pieces, you may move to any empty point at all.
• You lose when you have two pieces left, or cannot move. The computer plays the same rules.
• If thirty moves pass with no piece taken, whoever has more pieces wins; level is a draw.

Why the middle points win games

The twenty-four points are not equal. Four of them — the ones halfway along each side of the middle square — sit on four lines each, while the corners of any square sit on two. A piece on a four-line point is part of twice as many potential mills and, more importantly, has four places to go. In the sliding phase, mobility is the whole game: a side with pieces boxed into corners runs out of legal moves and simply loses, without ever being taken apart.

The move that decides most games is the double mill, sometimes called a running mill. If you can arrange two mills that share a piece, you can open one and close the other, then slide back — taking an opponent's piece every single turn while they can do nothing but watch. Setting one up during the placing phase is the strongest thing you can do, and blocking one is worth more than making a mill of your own.

The last thing worth knowing is when not to make a mill. Closing a mill early, in the placing phase, often forces you to break your own shape to open it again, and the piece you take may be worth less than the position you wasted. Strong play is usually about mobility and blocking first, and taking pieces second. If you like the shape of this, Checkers and Reversi are the other two board games here where position matters more than material.

More games

More from ♟️ Board games vs computer:

• Four in a Row — Beat the computer and it thinks one move deeper next game. How long can the streak last?
• Reversi — Flip your opponent's discs to your colour. Take the corners — and beware the squares beside them.
• Checkers — Captures are compulsory — which is exactly how you set traps. Beat it and it thinks deeper next game.
• Dots and Boxes — The opening doesn't matter — the endgame is everything. Whoever runs out of safe moves first loses.
• Sea Battle — Five ships hidden in a hundred squares. Sink them all — the only score is how few shots it took.

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