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Caïssa Britannia
Developer(s) Fergus Duniho
Release 2001

Caïssa Britannia, originally known as British Chess, is a chess variant created by Fergus Duniho in 2001. It stemmed from an idea he had to create a British-themed chess variant. The game features lions (represented by inverted queens), unicorns (represented by inverted knights) and dragons (represented by inverted bishops), pieces based on the heraldic animals of England, Scotland and Wales respectively. The game also features a royal queen, since the British monarch was a queen at the time of the variant's creation. In addition, Caïssa Britannia also took several inspirations from the castling move and Chinese Chess (xiangqi) for the Queen's restrictions. The Chess Variant Pages explains the reasoning for the variant's name:

"Although the name of British Chess directly reflects the idea behind this game, it will be less appropriate when the monarch is once again a King. Because of this, British Chess also bears the alternate Latin name of Caïssa Britannia. This name better reflects the Queen-centered nature of this game. This name suggests a royal Queen, as Caïssa is the name for the female personification of Chess, sometimes regarded as the muse or goddess of Chess, and Britannia is the name for the female personification of Britain. So both parts of the name suggest a female royal piece. In addition, Christian Freeling has already used the name Caïssa for another Chess variant with a royal Queen, setting a precedent for associating Caïssa's name with the royalty of the Queen. Also, the name of British Chess sounds like it belongs to a regional variant, along the same lines as Chinese Chess, Burmese Chess, etc. Yet this game is not a regional variant. In contrast, the name of Caïssa Britannia is more poetic and less regionally descriptive, suggesting a thematic association with Britain, which is all that is British about this game, without implying a British origin."

Movement of the pieces

  • The queen moves as she does in standard chess: an unlimited number of unobstructed squares in any direction, orthogonally or diagonally. Since she is the royal piece in Caïssa Britannia, she is subject to the same check and checkmate rules affecting the king in standard chess. The Queen may also not pass over a square where she would be in check, nor pass through check to reach a square. In addition, she may not face the enemy queen on the same file, rank or diagonal with no pieces in between them.
  • The prince consort, represented by the king, may capture by moving one space in any direction, or it may slide like a rook or bishop without capturing.
  • The lion, represented by an inverted queen, was created by British chess writer T. R. Dawson, who based it off the cannon from xiangqi. Like the cannon, the lion needs to jump over a piece in order to capture. However unlike the cannon the lion can move and capture diagonally as well as orthogonally.
  • The unicorn, represented by an inverted knight, combines the standard bishop with the nightrider. Therefore, it may move an unlimited number of unobstructed squares diagonally, or it may make consecutive knight jumps in the same direction.
  • The dragon, represented by an inverted bishop, was created by Fergus Duniho for the game. It may make as many consecutive unobstructed two-square leaps in a direction as it wishes.
  • The rook moves just like the rook from standard chess, except that it cannot castle.
  • The bishop may move as far as it can diagonally, just like a standard bishop, or it may move one square orthogonally without capturing. Fergus explains that this is because the Caïssa bishops are Anglican, and the standard chess bishops, who are Catholic, made a vow to stay on one colour, a vow which the Anglican bishops didn't make.
  • The knight is not present in the initial setup, but rather is offered as a promotion option for pawns. It moves exactly the same as a standard knight.
  • The pawn moves exactly the same as in standard chess, but may only promote to a captured piece (as in grand chess) or to a knight.


The Chess Variant Pages states the following tips, with slight editing:

"This game has three major pieces and four minor pieces. The major pieces are the unicorn, rook, and prince consort. The minor pieces are the lion, dragon, bishop, and knight. Against a lone queen, a queen plus any two minor pieces are normally sufficient for checkmate. The only combination of two minor pieces that cannot force checkmate are two dragons when they are both on dark squares or both on light squares. But this can happen only when a pawn promotes to a dragon, and this will rarely ever happen, since a pawn can always promote to something else, even if only to a knight. So, for practical purposes, we may just say that a queen and any two minor pieces are sufficient for checkmating the enemy queen. But that is not the end of it.

Unlike in chess, where one king may never fully trap another, one queen may trap another in a corner, which can allow a single minor piece to checkmate the trapped queen. This almost gives a minor piece the power of a major piece, but not quite, because trapping a lone queen would result in stalemate before the minor piece could move in for checkmate. For a queen and minor piece to checkmate a queen on their own, the opponent must have another piece that may move after the queen is immobilized, yet also be unable to stop the impending checkmate with this piece. The extra power that queen/minor piece combinations have in this game makes the minor pieces semi-major pieces rather than mere minor pieces. A semi-major piece is one that can checkmate an isolated, though not lone, royal piece with help only from one's own royal piece. An isolated royal piece is one that is cut off from support without being the only piece of its color on the board. Also, semi-major pieces differ in endgame utility. In this game, the bishop and knight have the most endgame utility of all minor pieces, followed by the dragon, with the lion having the least. But the overall value of a piece is measured not only in endgame utility but also in mobility and midgame utility. With all this in mind, let's look at the pieces, beginning with the major pieces.

The unicorn is probably the most powerful piece in the game. Of all the pieces, it is the only piece that can checkmate a queen without help from another piece. This makes it a super-major piece. Its long-range attacking ability is very useful. Its Achilles heel is that it is open to orthogonal attacks from the enemy queen. When it tries to maneuver around the queen at close range, the queen can keep moving to attack it rook-wise. So, despite its ability to force mate on an empty board, it sometimes can't force mate without help from another piece.

The rook has a long-range attack that is generally more powerful than any of the unicorn's long-range attacks, but it has only four directions of attack instead of the twelve available to the unicorn. It remains vulnerable to the queen's diagonal attacks.

The prince consort has no long-range attack, but it's very good at forcing mate when it's up close and protected. One advantage it has over the other major pieces is that it is invulnerable to long-range attacks from the enemy queen. A queen may capture a prince consort only from an adjacent space.

The lion is a very powerful piece during the mid-game, though its value may diminish in the endgame. The lion is the only piece in the game that can pin two pieces with the same line of attack. This makes it very useful for immobilizing enemy pieces for easy picking off by other pieces. It is also useful for opening up lines of attack for other pieces, because one way to stop a lion's attack is to move the screen piece out of the way. It is also good at forking pieces, because most pieces it attacks cannot jump over the screen to capture it. The pieces it is most vulnerable to are dragons and other lions. It is also vulnerable to the enemy queen when nothing stands between them.

The Anglican bishop is more powerful than the standard bishop, because it can move between dark and light squares, allowing it to cover the whole board.

For a piece that is limited to one quarter of the board, the dragon is surprisingly powerful. It is very useful for protecting spaces while remaining safely across the board behind other pieces. One good way to checkmate a queen is to move the prince consort next to the queen while protecting it with a dragon. When two dragons occupy the same rank or file, they can secure it about as well as a rook, sometimes better, because it will take two pieces to block them. Thus, two dragons working together can be very helpful in preventing the enemy queen from moving beyond her present rank or file. The dragon is also one of the best pieces for defense, because it can easily protect several pieces even when other pieces stand between them. Although the dragon is not the quarterback of this game, it is very useful for backing up and supporting attacks from other pieces.

Although the knight has no long-range movement, it can attack any piece but the unicorn or another knight without that piece being able to capture it."