Jetan Tournament Help

What is Jetan?

Jetan is the chess-like game played by the inhabitants of Barsoom (Mars) in the novels by Edgar Rice Burroughs (ERB). This application allows two people to play each other online, and to decide which of the movement, wagering and duelling options apply to each match.

Most of the background for this project came from the web pages by Larry L. Smith (LLS). I have used his suggestions for the naming conventions and abbreviations for the pieces, the game types, and the game recording system. You should visit his page for a more in-depth analysis of the game's rules and conventions than is presented here.

Overview of the Game System

The game system is designed to allow you to abandon a game at any point, then take it up again later. If at any point you think the game has crashed, or your view becomes corrupted, simply have your browser reload the page you are on and it will be rebuilt to reflect the current state.

To play the game, you will need a modern browser (see "Browser Compatibility" below) with JavaScript and Java enabled. You will also need to be able to access TCP port 8001 on, the game server. If you have difficulty communicating with the server (see "Comms Applet" below), it may be because you are passing through a corporate firewall which has blocked that port.

Joining the Tournament

To join the tournament, select the "register as a player" link. Fill out the form presented, and you will be ready to play right away.

Organising a Game

The main tournament page is broken into three sections (see below for details). The top section contains a list of your opponents, and the status of your games against them.

Click the "Suggest time" link for the game you want to organise. This will take you to a form which allows you to propose a date and time to your opponent. When you submit this, it will generate an email to your opponent, giving them the option to accept your proposal or make one of their own. You will receive an email from the game system once they have chosen.

You will also be able to use this system to propose a time to resume a game that was interrupted in progress.

Setting Up the Game

You can choose to start any game you like, without waiting for your opponent, although you will only be able to get through the first stage without them also being online. For this description, we'll assume that your opponent is online.

Game Start

Find the game you want to play in the "Your Games" section of the main tournament page. If the game is untouched, it will be marked as "Pending", and will have a link named "start". If your opponent has already started setting up, the game will be marked as "In Progress", and the link will say "resume". Either way, click on the link. This will take you to the Force Selection page.

Force Selection

There is a certain amount of ambiguity in ERB's description of the game. This allows the players to choose exactly how each of the pieces move; you and your opponent can choose the movement rules you each want without referring to each other. To simplify the process, a selection of "themed" presets are available. You can use one of the presets as-is, or choose to customise the pieces, by clicking on the relevant button. If you choose to use the rules as-is, you will be taken straight to the Game Rules Selection page.

A weak force costs less to field than a strong one. If you are confident in your playing ability, you can choose to field a weaker force, to minimise your points loss if your opponent should win.

Customise your Force's Rules

If you choose to customise your force, you will be given a list of each piece type, with radio buttons to select which rules they will use. The pieces' costs are given in the left-hand column, and will be updated as you change the rules. The overall cost for the force is given at the bottom.

Once you are happy with your force's rules, click Play with these rules to go to the Game Rules Selection page

Game Rules Selection

This page gives you your first view of your opponent's choice of force. (You can if you wish go back and change your own forces in reaction, using the [Change] link in the force header bar.)

It also gives a list of the game rules in play. (See below for more details on the rules themselves.) Starting with the Orange player, you and your opponent can take turns to suggest modifications to the rules, until you are both happy.

If you click the relevant button to make a change, the drop-down rule menus will become active, and you'll be given an input box to write a short comment to your opponent. When you submit your changes, your opponent will be given a summary of the new rules, along with your comment, and will have the opportunity to accept those rules or propose further changes.

Once you are both happy with the rules, you will be taken to the main game board to select the pieces you will play with.

Piece Selection

You and your opponent can now choose to remove some pieces from your forces. As with the rules selection, playing with a weaker force increases the risk of losing while decreasing the cost of doing so.

Simply click on the pieces you want to remove. They will be highlighted in blue, and your Ante will be decreased appropriately. If you want to add a highlighted piece back in, click on it again. Once you are happy, click on the long button to indicate your readiness to play.

You will notice that moving your pointer over a piece will cause a description of its moves to appear in the right-hand column. This gives you another opportunity to look at the details of your opponent's force.

Your opponent's choices will also be highlighted as they make their decisions. You can use the chat window to make any negotiations you require.

If your opponent changes their force after you have declared you are happy, you have the opportunity to make further changes in response. Only once both opponents are agreed on the forces will the game itself commence.

Playing the Game

Note: this document is an introduction to using the Jetan Emulator; it is not intended as a primer on the strategies of Jetan. For details on the nuances of the game itself, please see Larry L. Smith's web pages.

The Control Area (right hand column)

The bar at the top of the control area indicates whose turn it is, and what is expected of them. The buttons immediately below (which are only visible when their use is appropriate) are used to pass your move or trigger your Princess's Escape move. Underneath the buttons are your scores and the pot for the match. If you are using the "ransom" rule, these numbers will be updated as pieces are taken.

Below these displays are the piece information panel, the Game History panel, and the Chat window.

The Board

When it is your turn, you can select any of your pieces by clicking on it. This will cause the squares it can legally reach to be highlighted in blue. To move your piece, click on the highlighted square you want it to go to. To select a different piece, click on it instead. To cancel the move, click anywhere else on the board.

When your opponent moves, the moved piece and its original square will be highlighted in blue until you select a piece of your own.

Forced Escape

If your opponent attacks your Princess, control is immediately handed over to you. All squares that your Princess can legally Escape to will be highlighted in green. Once you choose the Escape square, control is handed back to your opponent while their move completes. If your Princess has already used her Escape move, or there are no squares she can legally reach, your opponent's move finishes immediately (as does the game).

Manual Escape

You can choose to make your Princess Escape without being attacked, by using the appropriate button. According to the rules you can do this at any time during the turn sequence; however there is currently a problem resolving manual Escapes during your opponent's turn (see Known Issues for details). When your opponent performs a manual Escape during their turn, both pieces moved are highlighted as above.



You can choose to Pass your move by clicking the appropriate button. While this tactic is most useful when movement requires an ante (a Game Rule currently disabled, since players in this tournament can't run out of money), it could still have some utility. The rules state that a player loses the game if they pass twice in a row; the button will change its text to "Resign" when clicking it would have this effect.



You can win the game by taking your opponent's Chief with your Chief, or by taking their Princess with any of your pieces.


Unless you have modified the Game Rules, you can force a draw by taking your opponent's Chief with any of your non-Chief pieces.


If neither player wins within 10 moves after they are both reduced to three pieces of the same value, the game is stalemated. If the three-pieces-each situation occurs, a message will be posted to the Chat window, and the top bar will reflect the number of moves remaining until the end of the game.

Game Over

Once the game is finished, you and your opponent's scores will be adjusted accordingly, and the top bar of the Control Area will turn into a button taking you back to the Main Page. The system will allow you to reload or revisit your game for up to an hour afterwards, to finish chatting with your opponent. After that time the game will be loaded in Snapshot mode (see below).

Main Tournament Page

The main page is divided into three areas.

Your Games

This section lists your performance against each of the other players. It's hoped you'll be able to play two games against each of them, as Orange and Black respectively. The list gives you links to arrange game times, and to start or resume games, and displays the results of completed games.

Leader Board

This section displays the rankings of each player, with the number of games played and won, and their agregate scores. Currently position is determined by number of wins, with score being used in the case of a tie; this may be reviewed later.

Game Progress Grid

This section gives an overview of which games have been played. It also gives links to allow you to view games that are completed or in progress, in Snapshot Mode.

Snapshot Mode

Clicking on any of the Game Progress Grid links will take you to a view of the current state of the board. It is not updated automatically when players make moves, but you can reload the page to get a fresh view. It also gives you the rollover piece descriptions and a snapshot of the game history.


Game Rules

Jetan is a game of wagering and combat, as well as one of strategy. However, this Tournament is set up in such a way that players can't run out of money, so certain wagering rules can't apply, and have been disabled. Those that are still available are detailed below.

Capture or Duel

Normally, the piece that is moving captures the one it lands on. Like the bloodthirsty Orange Martians, you can choose to have the pieces duel for possession of the square instead. When duelling, each piece has two random numbers between 0 and 8 added to its value. The piece with the larger total wins the duel; if the totals are the same, the process is repeated. The odds for this contest are:

in Value
Chance of
piece winning
in Value
Chance of
piece winning
050% 611%
142% 78%
234% 85%
327% 93%
421% 102%
Be wary of trying to win the game by dueling Chief against Chief! It could easily go against you.

The value of each piece depends on its abilities, see below for details.

Winner Takes All or Ransom

The Ante for each player is based on their force size and strength. You can choose to have the winner take the whole ante at the end of the game, or for each captured piece to pay their points values from the pot to the player that takes the piece. Using the Ransom rule, it is possible for a player to win the game but lose on points.

The ante can be anything from (depending on the piece values) 22 to 79: each player has an opportunity to reduce their ante by playing with some pieces missing.

Chiefs face Princesses or Each Other

This rule allows you to choose whether the Chief and Princess pieces sit left and right as viewed by their player, or as the King and Queen do in chess. Depending on the rules chosen for Chief movement, having them start facing each other can make Chief-on-Chief capture more difficult.

Pleb-on-Chief capture draws the game or not

Normally, capturing your opponent's Chief with any of your other (non-Chief) pieces forces a draw. You can choose to have the game continue instead. This is especially useful when duelling is enabled, since otherwise any attempt to take a piece with your Chief could end the game unexpectedly.


The Pieces' Moves and Values

I have given the pieces point values based on their flexibility of movement, ensuring that each improvement in ability matches an increase in cost:

  • Assume that the piece sits alone in the centre of the board.
  • Give points to the piece for each square it can reach, depending on the least number of steps it needs to take:
    • One step (or jumping): 30 points.
    • Two steps: 10 points per route, maximum of 30.
    • Three steps: 6 points per route, maximum of 30.
  • Divide the result by 120, and round to the nearest whole number.

The Princess also has an extra cost based on her Escape move. However, she automatically loses any duel she is in.

This system breaks down somewhat for the Chief and Princess, whose most expensive moves are assigned values to fit the 'increasing cost' model. This gives values rather different to the ones suggested by LLS, which make some piece variations unattractive by making them cost the same as more flexible versions.


Game History

As each game is set up and played out, the Game History panel will fill up with a description of the initial conditions and moves. The application uses the Technical Notation suggested by LLS, with a couple of extra devices. LLS asks that you send him your game notes, as he is compiling a reference work on the game. His email address is

Notation details

The first entries in the game history are the timestamp, the movement, capture and ante rules selected, and a description of the piece types (and unused pieces, if any) for each side. The actual play of the game then follows.

When describing a move, the ranks are numbered 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, beginning with the Black end; the files, beginning with the southern left, are lettered A-J. A move would be of the form "G2-G3".

When duelling is turned off, the usual notation for taking a piece is used: "G2xG3".
When duelling is turned on, the notation records the winner of the duel thus: "G2-G3(B)" or "G2-G3(O)".

When a Princess is forced to Escape by a piece landing on its square, the escape move is appended to the attacking move, thus: "G2-G3eA4".
When a Princess uses its Escape move by choice, the move is noted before the current player's move, thus: "(E0eJ5) G2-G3"

When a player chooses to pass, it is recorded thus: "---"

When the game is won, the last move has "C", "P", or "X" appended, depending on whether the game was won by Chief capture, Princess capture, or repeated passing respectively.

If the game is drawn, the last move has "d" appended.


Technical Details

Comms Applet

When playing the game, and during some setup stages, your browser communicates with the game system using a Java applet. This will appear as a small black rectangle with two flashing green and red lights at the bottom right of the page. If at any point either of the lights turns on permanently, there has been a problem with communications. Reloading the page will fix this in most cases. If the problem persists, there may be a firewall preventing you contacting the server, or there may be a more serious issue with the server itself. In the latter case, look for an announcement on the main game page.


Browser Compatibility

The system has been tested on Firefox 7, Chrome 14, and Internet Explorer 8. It should work on earlier versions of Firefox and Chrome, but will not work on Internet Explorer 6 (or earlier!) and may not display properly on IE7.

If you can report playing the game successfully on a different browser, or discover a problem with the game, please email us with the details.


Known Issues

If you start a voluntary Escape during your opponent's turn, it doesn't suspend your opponent's actions. If your opponent completes their move before you complete the Escape, your Escape move is used up, and the green highlighting doesn't clear until you select a piece (or try to Escape again). Fixing this problem currently has priority; for the moment, use the Chat window to politely ask your opponent to allow you to finish the Escape move before they proceed.

The history display of voluntary Escape moves could be formatted better.

There is a bug in IE8 which prevents the dynamic history displaying properly. It displays correctly when built statically, so reloading the page gets round the problem. (If anyone has a clue why 'white-space: pre-wrap' works when the page is loaded but not when the contents are changed dynamically, please email us!)



This Jetan simulator is copyright ©2004, 2011 Mad Elf under the GNU General Purpose License (see for details).