Two bishops on crossing diagonals mate a king that has castled queenside and been boxed in by its own pieces.
Why it matters
Two bishops on crossing diagonals can mate a king that has castled queenside and then boxed itself in with its own pieces. One bishop checks, the other covers the escape, and the rook and pawns the king trusted are the reason it cannot move.
It comes up far more often than it looks, because the queenside castled position naturally leaves the king on c8 or c1 with a rook on d8 or d1 and pawns nearby. The mating move is usually a bishop appearing from a distance on a6 or a3.
See it on a board
The bishops cross: one checks along a6–c8, the other covers b8 and c7, and Black's own rook and bishop take away d8 and d7.
Checked: this line ends in checkmate.
How to play it
- Look for an enemy king on c8 (or c1) with its own pieces on d8, d7 or c7.
- Clear the b7 square — very often by a queen sacrifice that the b-pawn has to accept.
- Check with the light bishop from a6, with the dark bishop already covering b8 and c7.
At each level
The same idea, said the way it is taught at each age.
Bishop · ages 5–7
Two bishops working on different colours can cover every square around a king. When the king's own pieces block the rest, that is mate.
Rook · ages 6–9
The typical route is a sacrifice on c6 or c3 that forces the b-pawn to capture, because that is what opens the diagonal for the mating bishop.
What goes wrong
- Checking with the bishop before the b7 square is clear, so the pawn simply blocks.
- Forgetting that the king can run to b8 if the dark bishop's diagonal is blocked.
Questions people ask
- Why is it called Boden's mate?
- After Samuel Boden, who finished a game in London in 1853 with the pattern. The queen sacrifice that opens the diagonal is the part everybody remembers.