Cham-gonu: Korea's Version of Nine Men's Morris

Nine Men's Morris is one of the most widely traveled board games in human history. Boards for it have been found cut into the roofing slabs of an Egyptian temple at Kurna — traditionally dated to around 1400 BCE, though some historians dispute how reliably that dating holds up — scratched into the deck planks of Viking ships, and cut into stone benches across the Roman Empire. Wherever people had a flat surface, a knife, and some spare stones, something very much like it tended to appear independently. Korea's branch of that family is called Cham-gonu (참고누) — and if you've ever played Nine Men's Morris, PlayGonu's Cham-gonu will feel instantly familiar, with a few distinctly Korean twists.

The shared core idea

Both games are played on a board of three nested squares connected by lines at their midpoints, giving 24 points total. Both split into two phases:

• Placement. Players alternate placing pieces (12 each in Cham-gonu, 9 each in the standard Western game — hence "Nine Men's") on any empty point.
• Movement. Once all pieces are down, players take turns sliding a piece to an adjacent empty point instead.

In both versions, lining up three of your own pieces in a straight line forms a "mill" and lets you remove one of your opponent's pieces from the board. Reduce your opponent to too few pieces to form a mill, or trap them with no legal move, and you win. If you know this shape from the Western game, you already know most of Cham-gonu.

Where Cham-gonu actually differs

Two things set the Korean version apart, and they genuinely change how the game plays:

• Diagonal corner connections. The standard Western board only connects the midpoints of each square's sides across the three rings — the corners are dead ends. Cham-gonu's board additionally connects the corners of all three squares diagonally, which means mills can form along those diagonals too. That's a meaningfully bigger set of threats to watch for than the Western game, and it opens up board geometry the standard version simply doesn't have.
• Twelve pieces instead of nine. More material on a board with more connections makes for a denser, more tactical middlegame — there's less open space to maneuver into, so positioning matters even more.
• A marked, permanently dead point after a capture during placement. In the Western game, a point that loses its piece to a mill just becomes empty again immediately. In Cham-gonu, that point is marked and can't be used for placement again for the rest of the placement phase — it only becomes usable once the game shifts to the movement phase. PlayGonu marks these with a small peg icon on the board so it's never a mystery why a point won't take a piece.

Why it's worth knowing both

Part of what makes "games built on a grid of lines with mill captures" so interesting is exactly this: the same core mechanic got reinvented, independently, by cultures that had no contact with each other, and each one added its own local variation. Cham-gonu's diagonals and dead-point rule aren't arbitrary — they're Korea's own answer to the same design problem every Nine Men's Morris–playing culture was solving. Playing both versions back to back is a genuinely good way to feel how small rule changes reshape an entire game's strategy.

Try it

PlayGonu's Cham-gonu is the site's main game — free to play in your browser, locally with a friend or against an AI with four difficulty levels, with the diagonal board confirmed against period reference diagrams.