Jetan, also known as Martian Chess, is a chess variant with unclear rules. It was created by Edgar Rice Burroughs as a game played on Barsoom, his fictional version of Mars. The game was introduced in The Chessmen of Mars, the fifth book in the Barsoom series. Its rules are described in Chapter 2 and in the Appendix of the book.
Board and pieces
Jetan is played on a black and orange checkered board of 10 rows by 10 columns, with orange pieces on the "north" side and black pieces on the "south".
Each player has the following playing pieces: one Chief, one Princess, two Fliers; two Dwars (Captains); two Padwars (Lieutenants); two Warriors; two Thoats (Mounted Warriors); and eight Panthans (Mercenaries). The Chief, Princess, Fliers, Dwars, Padwars and Warriors are positioned along the row closest to the player with the Chief at left center, the Princess at right center, and the Fliers, Dwars, Padwars and Warriors arranged to flank each, with the Fliers innermost and the Warriors outermost. The Thoats and Panthans are positioned along the next row out from the player with the Thoats flanking the Panthans. The complete arrangement of each side follows:
T p p p p p p p p T W P D F C P F D P W
Throughout the Internet there is seemingly much confusion regarding the play of this chess variant. The sole existing authority on Jetan being Edgar Rice Burroughs, with the finalized version of the rules presented in the Appendix of The Chessmen of Mars. This article attempts to match it.
Panthans are limited to one step per move: forward, diagonally forward and sideways. Other pieces take two or three. These may change their direction of movement at each step in the course of a move, so long as this is in a direction permitted for that piece. No piece can cross the same square of the board twice during the course of a move. The Princess and the Flier may jump over a piece that is in their path.
A capture is made when a piece lands on a square occupied by an opposing piece with its final step or jump; the Princess may not make such a move.
The pieces move as follows:
- Chief: three steps in any direction or combination of directions.
- This is equivalent to three moves of a chess king, except that it cannot double back and may only capture at the third step.
- Princess: three steps in any direction or combination of directions; it may jump over other pieces but cannot capture.
- It may make one ten space "escape" at any time during gameplay, jumping to any unoccupied space on the board.
- Flier: three steps diagonally; it may jump over other pieces.
- Per Burroughs, in an older version of Jetan these pieces were called Odwars.
- Dwar: three steps orthogonally.
- Padwar: two steps diagonally in any direction, or combination.
- Warrior: takes two steps in any direction or diagonally.
- Thoat: two steps, of which one is orthogonal and the other diagonal;"2 spaces, one straight and one diagonal in any direction")
- Panthan: one step in any direction except backwards or diagonally backward.
By analogy to standard chess, it is assumed that a piece that moves multiple squares can capture an opposing piece only by finishing its move on the opposing piece's square. In other words, a piece can capture only once per turn.
It is not explicitly stated in Burroughs' text that a piece entitled to a two-space or three-space move must move the full amount. For example, the Padwar at [P] is entitled to a two-space diagonal move. If it may move two spaces or less, then it could ends its move on any of the spaces marked  or . If it must move two spaces, then it must end its move on the spaces marked ; in this case, if all the spaces marked  are occupied by friendly or opposing pieces, or if all the spaces marked  are occupied by friendly pieces, then the Padwar is unable to move.
2 2 2 1 1 2 P 2 1 1 2 2 2
In Burroughs's description, Jetan is won when either a Chief captures the opposing Chief, or when any piece captures the opposing Princess. The game is drawn if each player is reduced to three or fewer pieces of equal value and it is not won within the next ten moves, or if a Chief is taken by any piece other than a Chief.
These rules result in too many draws for the tastes of most players so a number of variants have been proposed to address this issue, the simplest being that the capture of a Chief by a piece other than a Chief merely retires the Chief without drawing or ending the game.
Jetan in Burroughs's novels
According to The Chessmen of Mars, Jetan was said to represent an ancient war between the Yellow and Black races of Barsoom. This explains why the orange pieces begin on the "north" side and black pieces on the "south", because Barsoom's Yellow and Black races inhabit its north and south polar regions, respectively.
The second half of The Chessmen of Mars takes place in the city of Manator, where the most popular civil event involves human beings fighting to the death in a life-sized Jetan game viewed by hundreds of spectators. The "board" is large enough that some of the pieces are mounted on Thoats and yet still fit in a single "square". However, this life-and-death version departs from the rules of Jetan in one very significant way: When one piece lands on a square occupied by another, the first does not automatically replace the second. Rather, the two pieces fight to the death, and the winner of the sword fight wins the square. The lone exception involves the Princess: if one side's piece lands on a square occupied by the other side's Princess, no battle occurs, and the first side wins the game.
Similar games in other fiction
Burroughs's Jetan may have inspired authors of later planetary romances to invent similar extraterrestrial versions of chess fought with human beings. Instances of such homage include:
- Lin Carter's Darza, from Renegade of Callisto, eighth volume in his Callisto series
- Kenneth Bulmer's Jikaida, from A Life for Kregen, 19th volume in his Dray Prescot series
- John Norman's Kaissa, mentioned many times in his Gor series, although never fully described
- S. M. Stirling's Atanj, from In the Courts of the Crimson Kings, his own Burroughs-influenced novel of an alternate Mars, also not fully described
- George R. R. Martin’s Cyvasse from his A Song of Ice and Fire series.
- Warrior: The meaning of this move is opaque. The text says "straight in any direction, or diagonally, two spaces", whereas the Appendix says "2 spaces straight in any direction or combination". It is unclear whether this means that the piece may move two squares or must move two squares. From the text, this might mean moving like a chess king, but with twice the range; the text does not say whether the two steps must be in the same direction. From the Appendix, the result would be a pattern like this if two steps are required:
X X . X X . O . X X . X X
- Edgar Rice Burroughs finalized rules to Jetan in the Appendix to The Chessmen of Mars.
- Burroughs was explaining his chess rules for an Earth audience familiar with standard chess. He deliberately stated that the Princess and the Flier may jump over a piece that is in their path. The only reasonable interpretation is that the Chief, Dwar, Padwar, and Warrior are blocked by pieces in their path (as are the queen, rook, and bishop in standard chess). It is unreasonable to suppose that Burroughs could have meant that the Flier jumps over intervening pieces while the Chief captures all intervening pieces, as this would be so different from standard chess that he would have stated this, had it been his intention.
- Gollon, John (1968). "§28 Jetan (Martian Chess)". Chess Variations • Ancient, Regional, and Modern. Charles E. Tuttle Company Inc. pp. 209–13. LCCN 06811975.
- Handscomb, Kerry (Summer 2001). "Martian Chess". Abstract Games. Carpe Diem Publishing (6): 6–9. ISSN 1492-0492.
- Pritchard, D. B. (1994). The Encyclopedia of Chess Variants. Games & Puzzles Publications. pp. 155–56. ISBN 0-9524142-0-1.
- Pritchard, D. B. (2007). Beasley, John (ed.). The Classified Encyclopedia of Chess Variants. John Beasley. p. 133. ISBN 978-0-9555168-0-1.
- Jetan by Jean-Louis Cazaux, The Chess Variant Pages
- Jetan at BoardGameGeek