Black Narrows is played on a rectangular grid of size 2x2 or larger [each dimension is greater than or equal to 2], initially empty. Figure 1 shows a 5x4 grid. Mark Steere designed Black Narrows in August 2026.
Two players take turns placing black stones onto unoccupied points on the board, one stone per turn.
After your placement, there must be an orthogonally interconnected path of unoccupied points, of length at least 1, connecting every pair of stones. In Figure 2, the bottom left stone is connected to the top right stone by a path of unoccupied points marked with blue dots. The red dots mark some illegal placements. A stone placed there would not have access to the two stones on the left side.
The last player to place a stone wins. In other words, if you don’t have an available placement on your turn, you lose. In Figure 3, there are 9 stones on the board, an odd number, and there are no remaining placements available. Player 1 placed the last stone and has won the game.
I wanted an impartial game with single stone placement on a rectangular grid, and which was invulnerable to mirroring. Black Narrows was a solution. Black Narrows borrows a concept from another of my games, Narrows (May 2026).
Feel free to publish this rule sheet and to program the game of Black Narrows. No licensing fee or royalties are expected. However, please don’t change the name or the rules, and please attribute the game to me, Mark Steere. My other games can be found at marksteeregames.com.
Six computer levels. Level 1 places at random. Levels 2 to 5 think ahead with a Monte Carlo search, from a handful of random playouts at level 2 to several hundred at level 5. Level 5 also solves the position exactly once about two dozen legal placements remain. Level 6, Unbeatable, searches for three seconds before every placement and solves the position exactly as soon as it can, which is usually from the middle of the game on.
With Confirm placements on, a tap shows a translucent stone on the point you tapped. Confirm places it, and so does a second tap on the stone. A tap on another legal point moves the stone there. A tap anywhere else, on a placed stone, on an illegal point, between the points, off the board, or on the Undo button, takes the stone back. With Confirm placements off, a tap places the stone at once. Once a stone is placed, Undo takes back your last placement.
The line above the board counts the stones on the board and the legal placements left. When marking is on, a red dot marks every unoccupied point where a placement is illegal, as on the rule sheet. While a stone is waiting for Confirm, the red dots show the placements that would be illegal after it. A white ring marks the last stone placed. Hint marks the placement that level 6 would make. Record shows the game as text that you can copy.