It is believed that the special play known as “castling” first appeared in European chess in the 14th or 15th century. (The original version of the game did not have such a play.) Known then as the “king’s leap”, it allowed the king to move like a knight once. A later version of the king’s leap allowed the king to make two moves on his very first play but restrictions had been added: the king could not execute this move to capture an opponent’s piece and he could not use it to escape check. Furthermore, he was permitted to jump over an occupied square but could not jump over a square under attack. This later version is the predecessor of the modern castling which appeared in France early in the 17th century and then moved to England.
In modern chess, castling involves two pieces, the king and a rook, both of them still on their original square never having made a move. The king moves two squares towards the rook and the rook jumps over the king to take the square next to him. All in a single play, the king is moved to a safer location and a rook is brought closer to the middle of the board where it can more easily participate in the battle.
Castling is in many ways very unique as it is the only play where two pieces are moved at once, the only play where the king is allowed to move two squares, and the only play where the rook is permitted to jump over another piece. And then there are several restrictions to castling: the king may not be in check, the square the king passes through may not be under attack, the king may not place himself in check, there may not be any other pieces between the king and the rook, and neither the king nor the rook he is castling with may have made a move prior to castling. (This last rule implies that castling may only be executed once.)
Castling in Chess 99:
Castling does exist in Chess 99 but in a much-simplified form. It still involves two pieces, one of them being the king, and it can only take place with the two pieces in the first rank. But there end the similarities as the king may now castle with any piece, not just the rooks, he may castle repeatedly, not just once, and the play has altogether very few restrictions.
Castling is a play involving the king and one of his pieces.
Both pieces must be in the player’s first rank.
A king may castle with any of his pieces standing on the square right next to him. The two pieces simply exchange places. This version is referred to as “castling short”.
The king may also castle at a distance but only with his queen or one of his rooks, the only pieces that move horizontally. All intervening squares must be unoccupied. The king moves a single square towards the piece – rook or queen – he is castling with, and the said piece takes the original square of the king. This is “castling long”.
There are no other restrictions of any kind on castling.
Do note the following:
The king always moves a single square, even in castling. (This is simply the way the king moves and no exception is made for castling.)
The piece the king is castling with always takes the original square of the king.
The king may castle while in check. (One must keep in mind that doing so will automatically put the piece the king is castling with under a threat of capture.)
The king may castle and put himself in check. (But that is usually not recommended.)
Castling with a bishop will move the said bishop to the squares of the opposite color.
Neither the movement of the king prior to castling, nor that of the other piece he is castling with, matters.
Castling may take place anywhere in the player’s first rank.
It is never possible to capture a piece while castling.
Players may castle as often as they like.
Castling while in check is legal:
Black has played the queen to h1 and the white king is now in check. If white moves the king to the second rank to escape capture, the rook is definitely lost.
White castles instead attacking both the queen and the king! If black saves their king, white captures the queen and the game is lost for black. Black has little choice but to capture the rook. White captures the queen and the game is a draw from lack of material.
Another example of castling while in check:
Black has played the knight to f2 attacking both the queen and the king. If white plays the king, the queen is captured. If black plays correctly, they should win this game.
White castles instead. Black may still capture the queen but this time it will cost them their knight. This game is a draw.
Repeated castlings are permitted:
White opens this game by castling three times: first with the paladin, then with the bishop, and following the knight move to g3, with the rook. (Click on the right arrow to see the play unfold.)
One bishop is now on light squares, a rook has been brought closer to the center where the attack usually takes place, and the king has been moved to a safer location near the edge of the board. Furthermore, the king is now resting on a light square which offers protection from the opposing bishops (should they both remain on dark squares).
Admittedly, this may not be the best Chess 99 opening but it is nevertheless a possibility.
How to perform castling:
Players must be careful of how they execute castling. When castling in standard chess, the king is first moved two squares towards the rook – a move that is in itself illegal – and then the rook is made to jump over the king to take its place next to him. In Chess 99, castling with a piece standing next to the king is clearly unambiguous however it is executed. However, if castling long, one should never play the king first as the king moving a single square is very much, in itself, a legal move. To prevent any misunderstanding, it is the piece the king is castling with that should be picked up first. While still holding the piece in one’s hand, the king is moved a single square towards the original square of the other piece. The other piece takes the initial place of the king and that completes the castling. When castling in standard chess, the rook is made to jump over the king. When castling in Chess 99, the two pieces simply pass each other.
Note that it is probably a good idea to castle [at least] once early in the game. The king stands on a dark square initially and since both of the opposing bishops are also on dark squares, it is a rather vulnerable location for the king to be in. A major piece – queen or paladin – is then moved to the central file. They are in a better position to defend themselves against bishops since both queen and paladin move along the diagonals. And they are also better able to escape an attack since they both move in two different ways.
And there is one more consideration to keep in mind. Since the king is initially surrounded by his two major pieces, castling would hardly be an option should he become in check by a minor piece. (Since the piece the king castles with always takes his place, it would be a costly sacrifice.)