Boden's Mate: Two Bishops on Crossing Diagonals
Boden's mate is a checkmate by two bishops on criss-crossing diagonals, against a king whose remaining escape squares are blocked by its own pieces.
The mating picture
The textbook case is a king castled queenside. Picture a white king on b1 with a rook on a1 and a pawn on a2. A black bishop on a3 covers b2 and c1. A second black bishop gives check along the b1-h7 diagonal, from f5 or anywhere on that line, and also covers c2. The king's neighbors are a1, a2, b2, c1 and c2: two are blocked by its own pieces, and the bishops cover the other three.
The two bishops attack in an X shape, which is why it is sometimes called a criss-cross mate. The pattern is named after the 19th-century English player Samuel Boden.
It also works on the kingside. A king on f1 with its own pieces on e1 and e2 can be mated by a bishop on e3, covering f2 and g1, and a bishop checking from h3, which also covers g2.
The typical lead-in
Boden's mate needs open diagonals next to the king, so it usually follows a weakening pawn move such as b3 or c3, or a sacrifice that tears open the pawn shield. A queen sacrifice on c3 or c6 that is recaptured by the b-pawn is the classic way to open the a3-c1 diagonal.
Look for it whenever your opponent has castled queenside and moved the b-pawn. If one of your bishops can reach a3 (or a6) and the other can check along the long b1-h7 diagonal, the mate may already be there.
Why it gets missed
Bishops working from a long distance are easy to overlook, especially when one of them starts on its home square. Players also underestimate how few squares a castled king really has. Count them: on b1 there are only five, and two of them are usually filled by the king's own rook and pawn. Patterns like this one, missed in your own games, are the most useful ones to drill.
How to spot it
- Look for a castled king whose b-pawn (or g-pawn) has moved, opening a diagonal.
- Count the king's flight squares and note which are blocked by its own pieces.
- Check whether one bishop can cover the squares in front of the king from a3 or h3.
- Look for the second bishop's check on the other diagonal.
- Consider a sacrifice that forces a pawn recapture and opens the line.
Try one
Work it out from the diagram first, then play it on the board or open the solution.
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8hfd
cExample 1
Black to move and mate in two.
Show solution
12...Ba3+ 13.Kb1 Bf5#
White's b3 has opened the a3-c1 diagonal, and Ba3+ uses it: the bishop checks the king on c1 and covers b2. After Kb1, Bf5# checks along the f5-b1 diagonal and covers c2. The king is surrounded: a1 and a2 are its own rook and pawn, b2 and c1 belong to the bishop on a3, and c2 to the bishop on f5. If White plays Kc2 instead, Bf5 is still mate.
Position from a real game, via the Lichess puzzle database.