Nine Men's Morris (Mill)

Nine Men's Morris, also known as Mill, Merels, or Mühle, is one of the oldest known board games. Two players each have nine pieces, which they place and then move on a board consisting of three concentric squares connected by lines at the midpoints. When a player forms a row of three pieces along a line (a "mill"), they may remove one of the opponent's pieces from the board. The goal is to reduce the opponent to two pieces (making them unable to form mills) or to block all their moves.

Rules

1. The board has 24 intersections arranged as three concentric squares connected at the midpoints of their sides.
2. Each player has 9 pieces (stones) of their own color.
3. Phase 1 — Placing: Players alternate placing one piece on any empty intersection until all 18 pieces are on the board.
4. Phase 2 — Moving: Players alternate moving one of their pieces along a line to an adjacent empty intersection.
5. Phase 3 — Flying (optional rule): When a player is reduced to 3 pieces, they may move (fly) to any empty intersection, not just adjacent ones.
6. Forming a Mill: When a player forms a straight line of three of their pieces along a board line, they have formed a mill and must immediately remove one of the opponent's pieces.
7. Pieces that are currently part of a mill may not be removed unless no other pieces are available.
8. A mill may be "opened" and "closed" repeatedly — moving a piece out of a mill and back in on a later turn counts as forming a new mill.
9. A player wins by reducing the opponent to 2 pieces or by blocking all of the opponent's possible moves.

Strategies

• Control the Intersections: The intersections connecting the three rings (the midpoints of the sides) are the most valuable positions. They connect to four adjacent intersections, offering maximum flexibility.
• Double Mill (Pendulum): Create a configuration where moving one piece out of a mill simultaneously forms another mill. This allows you to remove an opponent's piece every turn — a devastating advantage.
• Block Opponent's Mills: Pay attention to your opponent's two-in-a-row formations and block them before the third piece completes the mill.
• Placement Phase Strategy: During the placing phase, focus on setting up potential mills and controlling key intersections rather than forming mills immediately. The placement phase largely determines the outcome.
• Keep Pieces Connected: Isolated pieces are less useful. Keep your pieces in groups where they can support each other and threaten mill formations.
• Reduce to Three: If your opponent is reduced to three pieces and the flying rule is active, don't despair — a player with three pieces has enormous mobility but lacks the numbers to form mills easily. Restrict their options.

Nine Men's Morris is one of the oldest known board games in human history. Game boards have been found carved into stone at ancient sites throughout the world. The earliest known board was discovered at the Kurna temple in Egypt, dating to approximately 1400 BCE. Boards have also been found at Bronze Age sites in Ireland, Viking burial sites in Scandinavia, and carved into cathedral cloister benches across medieval Europe.

The game was enormously popular during the Roman Empire, where it was known as "Terni Lapilli" or "Ludus Latrunculorum" (though scholars debate whether these names refer to exactly this game). Boards carved into the flagstones of the Roman Forum and other public buildings suggest it was a common pastime. The game remained popular throughout the medieval period in Europe, mentioned in Alfonso X's "Libro de los Juegos" (Book of Games) in 1283, one of the oldest books about board games.

The name "Morris" is unrelated to the English surname or Morris dancing. It likely derives from the Latin word "merellus" (a game piece or counter), which evolved into "merels" in Middle English. In German, the game is called "Mühle" (mill), and in many languages the name relates to the concept of forming a line or mill of three pieces.

In 1993, Ralph Gasser computationally solved Nine Men's Morris, proving that the game is a draw with perfect play from both sides (without the flying rule). With the flying rule for three remaining pieces, the game's complexity increases, but the standard version without flying is fully solved. Despite being solved, the game remains engaging for human players because the number of positions (roughly 10 billion in Phase 2) is far too large for casual memorization. The game continues to be played around the world, particularly in Europe and parts of Africa, and digital versions are widely available.