Nine Men's Morris Mill Captures: Which Stone Can You Remove?

Check the opposing stones after forming a mill

Nine Men's Morris mill captures depend on the opponent's current arrangement. Three of your stones along a marked straight line form a mill and let you remove an opposing stone. If any opposing stone stands outside a mill, your removal must come from those unprotected stones.

If every opposing stone on the board belongs to a mill, you can remove one from a mill. Heritage Ireland's rules state this exception. The examples below use ProjectGAMR's local two-player version, checked on November 6, 2026, and reach both situations during the placement phase.

Number the points and build the first position

Each square ring has four corners and four side midpoints. Count clockwise from its upper-left corner. Number the outer ring 1–8, the middle ring 9–16 and the inner ring 17–24. Points 1, 2 and 3 therefore run across the outer top edge.

Start a new game. Place stones at 1, 9, 2, 10, 4 and 11 in that order, alternating Lime and Violet. Violet's placement at 11 completes the middle top mill, 9–10–11. As Violet, remove Lime's stone at 4.

Continue by placing Lime at 5, Violet at 12 and Lime at 3. Lime now has the outer top mill, 1–2–3, and must choose a capture. Violet occupies 9, 10, 11 and 12.

Find the stone outside the protected row

Violet's 9–10–11 row is a mill. Point 12 stands alone on the right side of the middle ring. It does not belong to a completed Violet line, so it supplies the legal capture.

Try selecting Violet's stone at 9 while the capture prompt is active. The position stays unchanged because an unprotected target exists at 12. Select 12 instead to remove that stone. The game then announces Violet's placement turn. Complete this removal before continuing the placement sequence.

Continue until Violet has two complete mills

From that position, place Violet at 17, Lime at 6, Violet at 18, Lime at 8 and Violet at 19. Violet has completed the inner top mill, 17–18–19, and can remove a Lime stone. Choose the Lime stone at 8.

Lime now places at 4, completing the outer right mill, 3–4–5. The capture prompt appears again. Lime now occupies outer points 1 through 6. Violet occupies 9, 10, 11, 17, 18 and 19. Inspect Violet's two top rows before choosing a target.

Apply the exception to the whole board position

All six Violet stones now belong to mills. Points 9–10–11 form one, and 17–18–19 form the other. There is no Violet stone outside either completed line. Lime can therefore select point 9 and remove it, breaking the middle top mill.

Compare point 9 across the two checkpoints. Its surrounding row was complete both times. The legal capture changed because Violet's other stones changed. The first position included the unprotected stone at 12. In the second, every Violet stone already on the board was protected, activating the exception.

Recheck protection after a removal

After point 9 is removed, Violet's remaining stones are 10, 11, 17, 18 and 19. The inner top row stays complete, but points 10 and 11 have lost their third partner. If that arrangement appears at another capture decision, those two stones supply the outside targets.

The exception can apply during placement even while the opponent still has stones waiting to enter play, as the second example shows. Read the active prompt and the stones currently on the board. Choose New game, then follow the placements from the beginning to compare the two capture decisions.