Pillsbury's mate

The pattern usually appears against a castled king, meaning a king that has completed castling, the joint move of the king and one rook. In Pillsbury's mate, a rook gives the final check on an open file, a vertical line with no pawns interrupting its attack. A bishop controls the corner square to which the king would otherwise escape.

The defender's own pieces or pawns usually occupy the remaining exits. The rook does not have to stand next to the king: its attack line must be clear, and the bishop must close the corner. If a piece can interpose, capture the rook, or free a safe square, the position is not mate.

File check, closed corner

8

7

6

5

4

3

2

a1

b

c

d

e

f

g

h

The rook on g1 checks along the entire g-file with no intervening pieces.

The rook attacks and the bishop denies the corner

The roles are separate: the rook checks on an open file, the bishop closes the corner, and the black pieces seal the remaining squares.

1. The rook on g1 checks along the entire g-file with no intervening pieces.
2. The bishop on e5 controls h8 along the e5-f6-g7-h8 diagonal and denies the corner.
3. The rook on f8 and the pawns on f7 and h7 occupy the king’s other escape squares.

To recognize the pattern, separate three jobs: the rook attacks on the file, the bishop controls the corner, and defending pieces block the rest. Compare Mayet's mate, whose central picture is a rook beside the king directly protected by a distant bishop.