Triangular Chess is a chess variant for two players invented by George R. Dekle, Sr. in 1986. The game is played on a hexagon-shaped gameboard comprising 96 triangular cells. Each player commands a full set of chess pieces in addition to three extra pawns and a unicorn.
The starting setup is as shown. As in chess, White moves first and the object is checkmate. Other standard conventions apply as well, including castling, a pawn's initial two-step option, en passant, and promotion at the last rank. But the triangular geometry implies special move patterns for the pieces.
- A rook moves in a straight line starting through a cell edge. (Three directions are possible.)
- A bishop moves in a straight line starting through a cell vertex. (Three directions.)
- The queen moves as a rook or bishop. (Six directions.)
- The king moves one step as a queen. When castling, the king slides two cells if castling short (0-0); three cells if castling long (0-0-0).
- A knight moves in the pattern: two steps as a bishop, then one step as a rook in an orthogonal direction. A knight leaps any intervening men.
- The unicorn moves in the pattern: two steps as a rook, then one step as a rook in an orthogonal direction. Like a knight, the unicorn leaps any intervening men.
- A pawn moves straight forward one step at a time, whether crossing a cell edge or vertex. On its first move it may optionally move two steps straight forward. A pawn captures to either cell adjoining the cell immediately in front, in the same rank.
- If a pawn reaches a board edge where no step straight forward exists, the pawn continues to advance toward promotion using its capture move (whether there are men to capture or not).
Tri-Chess is a variation of Triangular Chess created by Dekle in the same year. The game is for two players and is the same as Triangular Chess in all respects except the moves of the bishop, rook, queen, and king are increased.
- A bishop moves in six directions constituting board diagonals.
- A rook moves in six directions along horizontal ranks or oblique files.
- The queen moves as a rook or bishop. (Twelve directions.)
- The king moves one step as a bishop or two steps as a rook.
- Also by George Dekle:
- The notation system used identifies each cell by its horizontal rank (letter) and the intersection of two oblique files (two numbers).
- Pritchard, D. B. (1994). The Encyclopedia of Chess Variants. Games & Puzzles Publications. ISBN 0-9524142-0-1.
- Pritchard, D. B. (2007). Beasley, John, ed. The Classified Encyclopedia of Chess Variants. John Beasley. ISBN 978-0-9555168-0-1.