King + Rook vs King, the Box
King and rook against a lone king is a win, and the rook builds a box that shrinks until the king reaches the edge with no escape square. The rook cuts the king off on the back rank, and the white king takes the remaining escape squares.
The finished shape
This is the finished shape. King and rook against a lone king is a win, and the rook builds a box that shrinks until the king reaches the edge with no escape square.
FEN: k1R5/7p/1K6/8/8/8/8/8 b - - 1 1
a b c d e f g h
8 k . R . . . . . 8
7 . . . . . . . p 7
6 . K . . . . . . 6
5 . . . . . . . . 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 . . . . . . . . 2
1 . . . . . . . . 1
a b c d e f g hThe worked example
White plays the mating move here. The rook cuts the king off on the back rank, and the white king takes the remaining escape squares.
FEN: k7/7p/1K6/8/8/8/8/2R5 w - - 0 1
a b c d e f g h
8 k . . . . . . . 8
7 . . . . . . . p 7
6 . K . . . . . . 6
5 . . . . . . . . 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 . . . . . . . . 2
1 . . R . . . . . 1
a b c d e f g hHow to prevent it
Black plays h6 first. The pawn move opens an escape square, so the mate no longer works.
FEN: k7/7p/1K6/8/8/8/8/2R5 b - - 0 1
a b c d e f g h
8 k . . . . . . . 8
7 . . . . . . . p 7
6 . K . . . . . . 6
5 . . . . . . . . 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 . . . . . . . . 2
1 . . R . . . . . 1
a b c d e f g hKey points
- The rook cuts the king off on the back rank, and the white king takes the remaining escape squares.
- The worked example ends with Rc8.
- To prevent it, keep the king near the centre and do not get driven to the edge.
- Attack the rook when it steps too far from its king, so the box cannot shrink.
- Count the box before each rook move, because one square of space lets the king slip out.
- This shrinking-box method is called the box mate.
Try it Yourself
Edit the code, then press Run.
Running is simulated · Rust Playground
Exercise
Find the checkmate in this position.