Grande Acedrex
Grande Acedrex — starting position
https://engine.moddable.games/play/?game=chess&variant=grande-acedrex
Grande Acedrex (Spanish: “Great Chess”) is a large medieval chess variant documented in the Libro de los Juegos (Book of Games) commissioned by King Alfonso X of Castile, c. 1283. It is played on a 12×12 board with six exotic piece types drawn from mythology and natural history as understood in 13th-century Spain. Rules are reconstructed from the Alfonso X manuscript as described by Murray, Gollon, and Pritchard.
The Board
12 files (a–l) × 12 ranks = 144 squares.
Starting Position
Each player has 12 pieces on their back rank and 12 pawns on rank 4. Ranks 2–3 (White) and ranks 10–11 (Black) are empty at the start.
White (rank 1): Rook a1 · Lion b1 · Unicorn c1 · Giraffe d1 · Crocodile e1 · King f1 · Griffion g1 · Crocodile h1 · Giraffe i1 · Unicorn j1 · Lion k1 · Rook l1
White pawns (rank 4): a4–l4
Black (rank 12): Rook a12 · Lion b12 · Unicorn c12 · Giraffe d12 · Crocodile e12 · King f12 · Griffion g12 · Crocodile h12 · Giraffe i12 · Unicorn j12 · Lion k12 · Rook l12
Black pawns (rank 9): a9–l9
Pieces
| Piece | Movement |
|---|---|
| King | One square in any direction. On its first move only, may leap two squares horizontally, vertically, or diagonally. |
| Rook | Slides any distance horizontally or vertically. |
| Griffion | Steps one square diagonally, then slides any number of squares horizontally or vertically. Cannot jump. The diagonal step must come first; the piece may also stop after just the single diagonal step. |
| Unicorn | First move: leaps as a Knight (cannot capture on this move). All subsequent moves: slides any distance diagonally (as a modern Bishop). |
| Lion | Jumps exactly 3 squares horizontally or vertically. Jumps over intervening pieces. |
| Giraffe | Leaps: one diagonal step then three squares horizontally or vertically — a (1,4) displacement from the starting square. Jumps over intervening pieces. |
| Crocodile | Slides any distance diagonally (as a modern Bishop). |
| Pawn | Moves one square forward. Captures one square diagonally forward. No double first step. |
Promotion
A pawn reaching the last rank promotes to the piece type that occupied that file in the opening setup — except on file f (the King’s file), where it promotes to a Griffion. Promotion chart for White reaching rank 12:
- a12 or l12 → Rook
- b12 or k12 → Lion
- c12 or j12 → Unicorn
- d12 or i12 → Giraffe
- e12 or h12 → Crocodile
- f12 or g12 → Griffion
Special Rules
- No castling.
- No double pawn step.
- Stalemate: A player who stalemates the opponent wins.
- Bare King: Capturing all of the opponent’s pieces except the King is a win. Exception: if the opponent can also bare the other King on the very next move, the result is a draw.
Attribution
Grande Acedrex is documented in the Libro de los Juegos by Alfonso X of Castile, c. 1283. Rules from chessvariants.com/historic.dir/acedrex.html (Hans Bodlaender, from Murray, Gollon, and Pritchard).