Design

The board design is inspired by the ancient Citadel chess.

For the first time in the chess history, the “Citadel” class of chess variants are explained in the book of “Precious Arts” in 1339, written by an Iranian philosopher and scientist Shamseddin Mohammad ebn-e Mahmood-e Amoli, known as “Amoli”.
In his book, Amoli recalls this class of chess variants as Shatranj-al hosun, or in Persian: Shatranj-e hosun. The word “Hosun” means Citadels and Shatranj-al hosun literally means citadel chess. This variant is also described by John Gollon’s book “Chess Variations: Ancient, Regional, and Modern” which are played for more than a thousand year in Iran and other middle eastern countries.

In the book of “Precious” Arts which is kept in the meuseum of art and culture in Tehran, Iran, by registration number 816353, page 634, writer describes citadel chess as follows:
“It is a hess game that is played on a 10 by 10 board, with 4 additional squares in the corners, called citadel. If the king goes to the citadel squares of the enemy, nothing attacks him unless he goes out of the citadel squares. In this game if pawn passes enemy pawn, it can be captured diagonally.”

As we see here, Amoli not only describes citadel chess board and rules clearly, but also mentions another important chess rule which is originated in citadel chess: The “en passant” move.
Although the Citadels class of chess is being played rarely in Iran and middle east nowadays, but traditionally in almost all the handicraft chess board (called “Khatam” chess boards) which are made today in Iran, the Citadel squares are still clearly present. However not everyone knows that these Citadel colorful squares are more than just an artwork and they represent the tradition of playing Citadel on a normal chess board, a tradition that has been lost in time and more importantly, by the “standardization” of chess by the international federation FIDE.
Another aspect of chess that we have lost by such western “standardization” is the fact that chess has never been ONE game in India and Iran, but it was “a CLASS of games”,  with many different variants and start positions that were played, wisely selected, for specific occasions: being a war, or peace, or a celebration or pray, or even one’s medium for hours of meditation.
This is just a personal opinion (and of course debatable) that so much “standardization” of chess and one’s overdoing the well-known-to-everyone openings of FIDE chess again and again (and even worse: memorizing the moves), is actually defeating the purpose of this game, which is finally increasing one’s ability to meditate and make an accurate judgment in an absolutely unfamiliar situation in one’s life, which is abstractly represented as a “position” in this game.
Chess is not here for us to study and memorize openings to “win” the game (to achieve what exactly?) but is here for us to train and increase our thinking and analyzing abilities to solve the real-life problems. In that respect, chess is the most abstract representation of life.

In the picture below you can see some of these beautiful Iranian handmade chess boards (note the Citadel squares and that not all of them consist of “dark” or “light” colored squares, but are simply highlighted by different “Khatam” patterns):

Khatam chess boards

Other games inspired by Citadel Chess are Mini Citadel (designed by A.J. Winkelspecht) and the most recently, Omega chess (designed by Daniel MacDonald). There is however a fundamental difference the above mentioned 3 Citadel games and Persian Chess:
All those Citadels boards consist of even number of Files and Ranks (10-12 in historical Citadel and Omega and 8-10 in Mini Citadel), which means the 4 Citadel squares (corner squares) cannot be attacked by one piece at the same time and there is at least 2 pieces needed to attack them simultaneously. There is no center square present in Citadel, Mini Citadel or Omega.
Below you see the board design and start positions of the Citadel variants:

Citadel variants

References:
– John Gollon’s “Chess Variations: Ancient, Regional, and Modern” (in Google books)
– Citadel chess (in chessvariants.org)
– Mini Citadel chess (in chessvariants.org)
– Omega chess (in chessvariants.org, official website: omegachess.com)
– Chess 911 (previous publication of Persian chess, in chessvariants.org)

Persian chess board (85 squares)

In Persian Chess (consist of 9 Files and Ranks internally, and 11 files and ranks including the corner squares) the number of Files and Ranks are odd (9 and 11), therefor the board has a an specific characteristic which is the Center square: e.g a dark square Bishop or a Bishop compound piece can attack all 4 corner squares simultaneously, therefore a dark square bishop in this game has higher value than a light square bishop: the value of a dark square bishop is 4 pawns and the value of a light square bishop is 3.5 pawns.
The Center square is not off-board in Persian chess, therefore the board consists of 85 active squares and 36 off-board squares (total 121 square). After playing some games you will see this center square gives Persian Chess very specific characteristics which is not present in any other Citadel game, this 121 squares board design is presented in the following diagram where square numbers are shown as 0 to 120:

Persian Chess: board design

board design and center square

For those who are interested, from the programming perspective, a 121 square board (85 active squares and 36 off-board squares) is not to be defined “as is” for the engine because we also need so-called “sentinel” files and ranks to determine if a piece is moved out of the board during the move generation, therefore the Persian Chess board which is actually programmed for the current engine, consists of 195 squares instead of 121 squares [Dan Spracklen, Kathe Spracklen  First Steps in Computer Chess Programming – 1978] The sentinel squares is not visible for human and it is only used internally in the chess engine. The actual board matrix in programming the engine is shown in the diagram and code section below:

 sentinel squares

var variant = "Persian"
var PIECES =  { EMPTY : 0, wP : 1, wN : 2, wB : 3, wR : 4, wS : 5, wF : 6, wQ : 7, wK : 8, bP : 9, bN : 10, bB : 11, bR : 12, bS : 13, bF : 14, bQ : 15, bK : 16 };
var PIECE_NAMES = ['EMPTY', 'wP', 'wN', 'wB', 'wR', 'wS', 'wF', 'wQ', 'wK', 'bP', 'bN', 'bB', 'bR', 'bS', 'bF', 'bQ', 'bK'];
var PieceVal= [ 0, 100, 325, 325, 550, 750, 900, 1000, 50000, 100, 325, 325, 550, 750, 900, 1000, 50000  ];
var BRD_SQ_NUM = 195;

// wS, bS = Persian Princess (white, black)
// wF, bF = Fortress (white, black)

It also needs to be mentioned that 9×9, the number of internal squares in this variant, by itself is not unique at all, and there are many other variants based on a 9×9 chess board. Most important 9×9 variants are Shogi (Japanese Chess), Perfect Chess, Modern Shogi, N by N Chess variants, Ministers Chess and Chimerical Chess to name a fewso there is absolutely no claim here about ‘inventing’ a 9×9 board design; such a claim would be ridiculous: only Shogi is being played by mankind for more than 800 years. That is more or less the reason this variant has been initially named and published as Chess911. The original Chess911 game rules still lives here as the Egyptian Eye sub-variant.

In the program you will find different level of training (so-called “handicap” positions) which might help you to get a bit familiar with this game in the beginning and win the game easier. Using this option you can basically remove some pieces from the black army. This option, in 5 different levels, gives advantage to white player. (click on the picture below to start the game)

handicap positions