Triangle Mate

The Triangle Mate is a checkmate against a king on the back rank, delivered by a queen and a rook together: the queen checks from right beside the king, and the rook, on the queen's rank, both defends that queen and blocks the king's last escape square. It is named for the triangle formed by the three pieces - king, queen, and rook.

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Key square

Why it is mate

The f8 king is on the back rank, so it has five neighboring squares: e7, e8, f7, g7, and g8.

• f7, g8: the checking g7 queen covers both. Sitting right beside the king, it covers f7 along the seventh rank and g8 along the g-file.
• e8: the e7 rook covers this down the e-file. The queen cannot reach e8 from g7, so only the rook can seal this square.
• g7: the queen stands here giving check. Kxg7 is illegal because the e7 rook defends it.
• e7: the rook stands here. Kxe7 is illegal because the g7 queen defends it.

Because the queen and rook defend each other, the king can capture neither. And the check is adjacent, so there is no room to interpose.

The rook's two jobs

In this pattern the queen handles the check and the squares in front of the king, and a single rook does the rest. The rook does two different jobs from one square: defending the queen and blocking e8. Place the rook elsewhere and the two roles come apart.

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Key piece

If the rook does not defend the queen, Kxg7 removes it. A queen checking from an adjacent square is only mate if the king cannot capture it.

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Key square

If the rook leaves the e-file, Ke8 opens up. Because the queen cannot reach e8 from g7, only the rook can block this escape. The e7 square in the main diagram satisfies both conditions at once: on the seventh rank it defends the queen, and on the e-file it blocks e8.

A real finish

Below is an actual position from our puzzle set. Black still has several pieces on the board, but the picture that traps the king is the same as the diagram above: the g7 queen checks the f8 king, and the e7 rook defends the queen while sealing e8.

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Key square

Black has a queen and a rook, yet nothing can save the king: there is no square to block the check, and neither white piece can be captured while they defend each other.

On this site

Our puzzle database has 340 problems tagged as Triangle Mate (counted September 2026). 50% (171) sit below rating 1200 and 9% (31) are rated 1900 or higher, so it leans toward the lower band without being purely a beginner pattern. It needs only a queen and a rook, but the rook has to land on the one square that both defends the queen and blocks the escape, which may be why it does not cluster at beginner level the way some other mates do.

Defending against it

• Get your king off the back rank in time. The pattern needs the king on the back rank. A pawn push that gives it luft helps only if the king can use it before the queen and rook arrive; once both stand on the rank in front of the king, as in the diagram, they cover every square it could step to.
• Attack the queen's defender. A queen checking from an adjacent square is only a threat while it is defended. Capture or drive off the rook that backs it up, and the king takes the queen, breaking the mate.
• Watch the square the rook needs. In this pattern the rook stands right next to the escape square it seals, so there is no room to put a piece in between. Keep that landing square covered before the rook gets there, or drive the rook away to win the square back.

References

• Lichess, puzzle theme Triangle mate (the source of this site's puzzle tags). https://lichess.org/training/themes
• Wikipedia, Checkmate pattern - the Triangle Mate. https://en.wikipedia.org/wiki/Checkmate_pattern
• Statistics produced by scripts/analyze-theme-stats.ts; the run is recorded in docs/data/triangleMate-stats.md.

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Related: Back Rank Mate · Dovetail Mate · All tactics