Detective's Rhombic Chess

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Detective's Rhombic Chess is a chess variant played on a board of 67 rhombi arranged in the following pattern:

Each rank extends from left to right, and each file extends from bottom‐left to top‐right. Note that some files only have spaces on odd‐numbered files.

Piece Movement

Due to the different geometry of the board, piece movement has to be changed in this variant.

Rook

The rook can move any number of spaces connected by edges.

Bishop

The bishop can move any number of spaces diagonally. Spaces are said to be diagonally connected if they share a corner and are the same color.

Queen

The queen has the combined moves of a rook and bishop.

Knight

The knight jumps one space orthogonally followed by one space diagonally, or one space diagonally followed by one space orthogonally.

King

The king moves to any space connected by an edge or corner.

This leads to the interesting property that a king can attack a queen without being in check.

Castling is not allowed.

Pawn

The pawn is the piece with the most complicated movement due to the non‐uniform space orientation and the pawn's requirement to always move forward. This results in it having two different movesets based on the orientation of the space it occupies. In the following diagram, move‐only destinations are marked in green, and capture‐only destinations are marked in red.

The pawn's double‐move and en passant rules are the same as in regular chess. En passant may only be performed with a capturing movement (the double‐move pictured above may be captured from c5 or f5, but not from d5). Pawns promote upon reaching their opponent's back rank to a Knight, Bishop, Rook, or Queen. Pawns staring into the void (white pawns on b7, d9, k7, and k9; black pawns on a5, a3, h3, and j5) do not promote, and do not have a special escape move; they may only advance by capturing. Thus, it is not advised (but not forbidden) to move your pawns to these spaces.

Board Setup

At the beginning of the game, pieces are arranged as follows:

Last revised by Em Nil.