Initial positionCaïssa is one of the 'Atlantis Triplets' that employ different implementations of the 'atlantis effect', the gradual disappearance of the playing area, eventually leaving one king or the other without refuge.
The other two are Shakti and Cyclix.

On top of that, Caïssa introduces another absolute novelty: 'capture by exchange', which is in fact no capture at all.

In the initial position the board is covered with 49 tiles.

  • All play is on the tiles.
  • Though tiles will be removed during play, the tile-complex must remain connected, that is, a tile or group of tiles must always remain orthogonally or diagonally connected to the rest.
  • White begins. Players move, and must move, in turn.

queenThe Queen
The king's role is played by the queen. The diagram on the left shows its options for movement and capture in a non-check situation.

queen in checkIf in check, it is restricted to adjacent squares, as shown in the diagram on the right. Thus pieces giving check from a distance, need no cover. The queen is the only piece with the power of capture in the usual sense.

The atlantis effect
If the queen moves, the tile it vacates is removed in the same turn. The removal is compulsory, but it may not violate the tile-connection rule.

The mutual check rule
Queens may not see one another along the same rank, file or diagonal, so neither player may effectuate that situation. Thus a Queen may protect a piece against capture by it's counterpart.

connection ruleThe pieces move as in Chess. Under the implicit condition of not putting its own queen in check and the explicit condition of not violating the connection rule, a piece can always move to any of its target-squares, whether or not it is tiled, and if it is, whether or not it is occupied, and if it is, regardless of the color of the occupying piece!

  • If the target-square has no tile, the piece takes its own tile with it. At the end of the move the tile-complex must still be connected. There is no 'during the move', so the knight may legally move to the square marked O.
  • If the target-square has an empty tile, the piece may simply move there.
  • If the target-square is occupied by a friendly piece, the player must exchange the pieces.
  • If the target-square is occupied by an opponent's piece, the player must also exchange the pieces, but there is one exception: a switch between two pieces of the same type may not in the next turn be 'undone' by the opponent.

connection ruleAbout tile-surfing and the connection rule
This 'mate in 1' shows another application of tile-surfing and the connection rule. For clarity all other pieces have been omitted.

After d2c4, the queen cannot move because the tile on c1 would be disconnected. If black were able to exchange the knight on c4 immediately with any of his pieces, he could yet prevent the mate, but the queen would remain immobile until one of black's pieces would bring a tile to the rescue.

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Example game























How I invented ... Caïssa
Using the Caïssa applet
External links


Caïssa © MindSports
Java applet © Ed van Zon