Double-bishop mate
Also known as Two-bishops attacking mate, Bishops' battery mate
Two bishops stand on neighbouring parallel diagonals and sweep the squares beside a king pinned to the edge. One bishop blankets the long diagonal into the corner; the other delivers check along the diagonal just next to it. With the attacking king guarding the last escape squares, the defender runs out of room.
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How it works
The two bishops cover adjacent, parallel diagonals so that between them they rake the whole edge. Here the dark-squared bishop on g7 owns the a1-h8 diagonal, sealing h8 and h6; the light-squared bishop on e4 owns the b1-h7 diagonal, checking the king on h7 and covering g6. The bishop check cannot be blocked (the diagonal is empty) or captured (the bishop is far away). The supporting king on f7 guards g8 and defends its own bishop on g7, so Kxg7 is illegal. Every escape square is taken, so it is mate.
How to spot it
Look for it whenever you have both bishops and the enemy king is shoved to the side or corner with little around it - classically at the end of a king-and-two-bishops endgame, but also after a kingside attack peels the pawns off a castled king. The trick is to put the bishops on adjacent diagonals (not the same one) so they cover two parallel lanes, then bring your own king up to plug the remaining squares before delivering the check with the second bishop.
Key ideas
- Two bishops on adjacent parallel diagonals cover the whole edge between them.
- One bishop seals the long diagonal; the other delivers the check.
- The attacking king must guard the escape squares the bishops cannot reach.
- A bishop check on an open diagonal cannot be blocked - only a flight square saves the king.
- First herd the king to the edge or corner, then close the net.
Famous example
The standard finish in king-and-two-bishops endgame technique: herd the lone king to the edge, then let the bishops mate on adjacent diagonals. The same two-diagonal sweep appears in attacks on a castled king stripped of its pawns.