Nine Men's Morris

How to Play

1. Placement phase: players alternate placing their nine pieces on empty board points.
2. Whenever three of your pieces form a straight board line, you create a mill and remove one opposing piece, subject to the game's mill restrictions.
3. Movement phase: after all pieces are placed, move one piece along a board line to an adjacent empty point.
4. Flying phase: when a player has only three pieces left, that player may move to any empty point.
5. A player loses when reduced below three pieces or when unable to make a legal move.

Understanding Mills

A mill is valuable not only because it removes an opposing piece, but because it can become a repeated threat. Opening and re-closing the same mill can force the opponent to defend continuously. Strong positions often combine two almost-complete mills so that one move threatens both.

Strategy Tips

• During placement, prioritize flexible structures rather than filling one line too early.
• Protect pieces that connect several possible mills.
• Avoid becoming immobile even if you temporarily have more pieces.
• When removing an opponent piece, consider mobility and future mill potential, not only immediate material.

Game-Theory Connection

Nine Men's Morris is a deterministic sequential game with changing action rules across phases. It is useful for studying state-space search, tempo, threat creation, zugzwang-like mobility problems and how the value of a move depends on future phases of the game.