Grid chess is a chess variant invented by Walter Stead in 1953. It is played on a grid board. This is a normal 64-square chessboard with a grid of lines further dividing it into larger squares. A single rule governs Grid chess: for a move to be legal, the piece moved must cross at least one grid line.
Grid chess is also used in chess problems.
Various arrangements of the grid have been tried, but the original, and by far the most popular, is that shown to the right, which divides the board into sixteen 2x2 squares.
In the sample position, White can play either a3 or a4, but cannot move his b-pawn. Black cannot play Bd5 but can play any other bishop move - if he wants to put his bishop on d5, it will take two moves (for example, first Ba8, then Bd5). The white king is not in check from the queen, but would be, if the queen were to take a step back with Qe3. The white king cannot take the queen, although the white knight can. The black king, on the other hand, is in check from the rook on c8. Black cannot escape check as he could in standard chess with Ke7 or Kf7, as these moves do not cross a grid-line. He can play Kd7, however, and also Kd8, bringing the king into the same large square as the rook.
It is possible to play entire games under Grid chess conditions, and a number of chess problems using Grid chess rules have also been composed. The one shown won first prize in the first Grid chess problem tournament. It is by H. Ternblad and was published in Fairy Chess Review, 1954. It is a helpmate in four (Black moves first and cooperates with White to checkmate him within four moves). The solution:
1. Ke2 Bc4+ 2. Kd3
- This brings the king into the same large square as the bishop, and so escapes the check.
- Withdrawing the bishop over a grid line gives check again.
3. Ke4 Bc6+ 4. Kd5
- Two kings can coexist next to each other so long as they are in the same large square.
This problem displays attractive correspondence between the paths taken by the king and bishop. It is worth noting the zigzagging path the black king must take to reach d5: the straightfoward route Kd1-d2-d3-d4-d5 is not possible because two of the moves do not cross grid lines, and Kd1-e2-e3-d4-d5 is not possible because on d4 the king is checked by White's king.