Check out Alice Chess, our featured variant for June, 2024.

This page is written by the game's inventor, Jose Carrillo.


Chess8400 is not a new game.

Chess8400 is the subset of 8,400 starting positions in Pseudo-Modern Random Chess where the Bishops start in opposite color squares.

The remaining 6,720 (of 15,120 total) Pseudo-Modern Random Chess positions have the Bishops starting on same color squares.

Chess8400 is really Fischer Random Chess (Chess960) played in a 9x9 board, with the The Prime Minister as the 9th piece, and an extra pawn.

Chess8400 is similar to Prime Ministers Random Chess played on a 9x8 board, but the board for the latter was inspired by Capablanca's Chess.



All pieces are randomly placed in the player's first rank, with two restrictions:

-Bishops start in opposite color squares.
-The King must be between the two rooks.

The opponents' pieces are placed with direct symmetry across the board (White's piece at a1 is equivalent to Black's a9, White's b1 to Black's b9, White's c1 to Black's c9, and so on)

Pawns (9 of them) are placed on each player's 2nd rank.

There are 8,400 different legal starting positions in Chess8400.


Orthodox Chess pieces are used, plus a Prime Minister (Bishop+Knight) and a 9th Pawn per side.

Approximate Value of the Pieces on a 9x9 board

Practical Value of the Pieces (adjusted to an 8x8 board)

Kings and their Prime Ministers from a 1968 Gabriel Vicente Maura's Modern Chess set:

Homemade Prime Ministers

Knight crowned by small Bishop, Bishop crowned with small Knight, and a crownless King.

Knights crowned with the heads of Bishops.

The Prime Minister is the only piece that is able to give a checkmate on it's own. Sample Prime Minister's checkmates:


External image links detected!

You know what would look worse on your page than this big, ugly warning? Broken image links. If you're the author, please make sure that doesn't happen to this page by replacing the following external graphic images with local copies.

    [0] =>
Most Orthodox Chess rules apply, including the objective of the game, the way pieces move and capture, en passant, check, checkmate, and the various draw situations (i.e. stalemate, insufficient mating material, threefold repetition, 50-move rule). Pawns may promote to a Queen, Minister, Rook, Bishop or Knight. Modified Castling rules are below.


The Chess8400 castling is long to either side of the board and the rules are based on the Modern Random Chess rules.

In Chess8400, depending on the pre-castling position on the castling King and Rook, the castling manoeuvre is performed by one of these four methods:

After castling, the rook and king's final positions are exactly the same positions as they would be in Gabriel Vicente Maura's 1968 Modern Chess. Thus, after c-castling (notated as O-O-Oc), the King is on the c-square (c1 for White and c9 for Black) and the Rook is on the d-square (d1 for White and d9 for Black). After g-castling (notated as O-O-Og), the King is on the g-square (g1 for White and g9 for Black) and the Rook is on the f-square (f1 for White and f9 for Black).

This table shows where the King and Rook end up and the notation for each type of castling.

White castles a-sidec-castlingO-O-OcKc1, Rd1
White castles i-sideg-castlingO-O-OgKg1, Rf1
Black castles a-sidec-castlingO-O-OcKc9, Rd9
Black castles i-sideg-castlingO-O-OgKg9, Rf9

However, castling may only occur under the following conditions, which are extensions of the standard rules for castling:

These rules have the following consequences:


Game Courier Preset


Game Courier Logs

Game Courier Logs for Games of Chess8400

To see actual games that have been played on-line, follow the link above.

Chess Variants by the Author:

Other Pages by the Author:

This 'user submitted' page is a collaboration between the posting user and the Chess Variant Pages. Registered contributors to the Chess Variant Pages have the ability to post their own works, subject to review and editing by the Chess Variant Pages Editorial Staff.

By Jose Carrillo.
Web page created: 2009-07-16. Web page last updated: 2009-07-16