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

Prime Ministers Random Chess

Esta es la versión en inglés de la página del Ajedrez Aleatorio del Primer Ministro.

Prime Ministers Random Chess (PMRC) is a new 9x8 variant inspired by Gabriel Vicente Maura's 1968 Modern Chess (9 columns, symmetric castling to either side, an extra pawn, the Prime Minister [B+N]) with the random concepts & the castling formula from Fischer Random Chess (FRC), but à la "Capablanca"! (on a board with the same number of ranks (8) as Ortodox Chess, but with more files (in this case 9) to accomodate the extra pieces [the Prime Ministers]).


Fischer Random setup of the pieces: symmetrical layout accross the board, with the restriction that Bishops start on opposite colors, and the King be placed somewhere between the Rooks to allow for the modified castling rule. Pawns go on each player's 2nd rank.

There are 8,400 possible starting positions!

The 9x8 board has dark squares at the corners on one of the 9-squares sides, and light squares on the other 9-squares side. It is irrelevant which side (White or Black) is playing with dark or light squares on their side.

You can play 9x8 Prime Ministers Random Chess on a 10x8 board (i.e. Capablanca Chess board) by covering the squares on the 'a' or 'i'-file; or on a 9x9 board (i.e. Modern Chess board) by covering the squares on the 1st or 9th rank.


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

Approximate Value of the Pieces on a 9x8 board

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

Gabriel Vicente Maura's Prime Minister (from his book Mathematical Thesis of Modern Chess):

Kings and their Prime Ministers

Homemade Prime Ministers

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

The Prime Minister is a piece able to give a checkmate on it's own! Sample Prime Minister's checkmates:


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. The modified Castling rules are below.


The PMRC castling rules are based in the Fischer Random Chess rules.

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

The castled position of the King would be equivalent to the Orthodox Chess Short-Castling (O-O), but to both sides of the board. Thus, after b-castling (notated as O-Ob), the King is on the b-square (b1 for White and b9 for Black) and the Rook is on the c-square (c1 for White and c9 for Black). After h-castling (notated as O-Oh), the King is on the h-square (h1 for White and h9 for Black) and the Rook is on the g-square (g1 for White and g9 for Black).

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

White castles a-sideb-castlingO-ObKb1, Rc1
White castles i-sideh-castlingO-OhKh1, Rg1
Black castles a-sideb-castlingO-ObKb9, Rc9
Black castles i-sideh-castlingO-OhKh9, Rg9

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

These rules have the following consequences:


This variation was invented by José Manuel Carrillo-Muñiz, from Puerto Rico, in May 2008.

Game Courier Preset

Prime Ministers Random Chess presets

Game Courier Logs

Game Courier Logs for Games of Prime Ministers Random Chess

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

Chess Variants by the Author:

Other Pages by the Author:

List of items authored by: José Carrillo

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: 2008-05-28. Web page last updated: 2008-05-28