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Castling
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Castling is a special move in the game of chess involving the king and either of the original rooks of the same color. Castling consists of moving the king two squares towards a rook, then moving the rook onto the square over which the king crossed. Castling can only be done if the king has never moved, the rook involved has never moved, the king is not in check, and the king does not cross over or end on a square in which it would be in check.
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Encyclopedia
Castling is a special move in the game of chess involving the king and either of the original rooks of the same color. Castling consists of moving the king two squares towards a rook, then moving the rook onto the square over which the king crossed. Castling can only be done if the king has never moved, the rook involved has never moved, the king is not in check, and the king does not cross over or end on a square in which it would be in check. Castling is considered a king move .
The notation for castling, in both the descriptive and the algebraic systems, is 0-0 with the kingside rook and 0-0-0 with the queenside rook. In PGN, O-O and O-O-O are used instead. Castling on the kingside is sometimes called castling short and castling on the queenside is called castling long; the difference being based on whether the rook moves a short distance (two squares) or a long distance (three squares) .
Castling is in most non-English speaking nations known as 'Rochieren/Rochada/Roque', while 'long/short castling' are used in those countries to refer to 'queenside/kingside castling'. Castling is a relatively recent European innovation in chess, dating from the 14th or 15th century. Thus, the Asian versions of chess do not have such a move.
Requirements
Castling is permissible only if all of the following conditions hold:
- The king must never have moved;
- The chosen rook must never have moved;
- There must be no pieces between the king and the chosen rook;
- The king must not currently be in check.
- The king must not pass through a square that is under attack by enemy pieces.
- The king must not end up in check (true of any legal move).
- The king and the chosen rook must be on the same rank.
It is a common mistake to think that the requirements for castling are even more stringent than the above. To clarify:
- The king may have been in check previously, as long as it is not in check at the time of castling.
- The rook involved in castling may be under attack.
- The rook involved in castling may move over an attacked square (a situation possible only with queenside castling).
Strategy
Castling is an important goal in the early part of a game, because it serves two valuable purposes: it moves the king into a safer position away from the center of the board, and it moves the rook to a more active position in the center of the board.
The choice as to which side to castle often hinges on an assessment of the trade-off between king safety and activity of the rook. Kingside castling is generally slightly safer, because the king ends up closer to the edge of the board and all the pawns on the castled side are defended by the king. In queenside castling, the king is placed closer to the center and the pawn on the a-file is undefended; the king is thus often moved to the b-file to defend the a-pawn and to move the king away from the center of the board. In addition, queenside castling requires moving the queen; therefore, it may take slightly longer to achieve than kingside castling. On the other hand, queenside castling places the rook more effectively – on the central d-file. It is often immediately active, whereas with kingside castling a tempo may be required to move the rook to a more effective square.
It is common for both players to castle kingside, and rare for both players to castle queenside. If one player castles kingside and the other queenside, it is called opposite castling. Castling on opposite sides usually results in a fierce fight as both players' pawns are free to advance to attack the opposing king's castled position without exposing the player's own castled king. An example is the Dragon Variation of the Sicilian Defence.
If the king is forced to move before it has the opportunity to castle, the player may still wish to maneuver the king towards the edge of the board and the corresponding rook towards the center. When a player takes three or four moves to accomplish what castling would have accomplished in one move, it is sometimes called artificial castling, or castling by hand.
Technical rules
Under the strict touch-move rules enforced in most tournaments, castling is considered a king move. A player who intends to castle but touches the rook first would be committed to make a rook move, and thus will not be permitted to perform the castling. Therefore, the correct way to castle is to first move the king. As usual, the player's mind may change between all legal destination squares for the king until it is released. When the two-square king move is completed however, the player has formally chosen to castle (if it is legal), and the rook must be moved accordingly. A player who performs a forbidden castling must return the king and the rook to their original places and then move the king, if there is another legal king move, including castling on the other side. If there is no legal king move, the touch-move rule does not apply to the rook .
It is also required by the official rules that the entire move be completed using only a single hand. Neither of these rules is commonly enforced in casual play, nor commonly known by non-competitive players .
The right to castle must be the same in all three positions for a valid draw claim under the threefold repetition rule.
Chess variants and problems
Some chess variants, for example Chess960, have modified castling rules to handle modified starting positions. Castling can also be adapted to large chess variants, like Capablanca chess, which is played on 10x8 board.
In chess problems, castling is assumed to be allowed if it appears possible, unless it can be proved by retrograde analysis that either the king or chosen rook has previously moved.
Notable castlings
- In this game between Yuri Averbakh and Cecil Purdy, Black castled queenside, and Averbakh pointed out that the rook passed over a square controlled by White, so it was illegal. Purdy proved that the castling was legal since this applies only to the king, to which Averbakh replied "Only the king? Not the rook?"
- Viktor Korchnoi, in his 1974 Candidates final match with Anatoly Karpov, famously asked the arbiter if castling was legal when the castling rook was under attack. The answer was in the affirmative, and Korchnoi ended up winning the game.
- Three castlings occurred in the game between Wolfgang Heidenfeld and Nick Kerins, in Dublin in 1973. Of course, the third one was illegal. See , "Greatest number of castlings".
- Tim Krabbé composed a joke chess problem containing vertical castling (king on e1, promoted rook on e8). The loophole in the definition of castling upon which this problem was based was removed by the new requirement that the castling rook must occupy the same rank as the king.
History
Castling has its roots in the "king's leap". There were two forms of the leap: (1) the king could move once like a knight, and (2) he king could move two squares on his first move. The knight-move could be used early in the game to get the king to safety or later in the game to escape a threat. This second form was used in Europe as early as the 13th Century. In north Africa, the king was moved to a safe square by a two-step procedure: (1) the king moved to the second rank and (2) the rook moved to the king's original square and the king moved to the rook's original square .
Before the bishop and queen acquired their current moves in the 16th Century they were weak pieces and the king was relatively safe in the middle of the board. When the bishop and queen got their current moves they became very powerful and the king was no longer safe on its original square since it can be attacked from a distance and from both sides. Castling was added to allow the king to get to a safer location and to allow rooks to get into the game earlier .
The rule of castling has varied by location and time. In medieval England, Spain, and France, the white king was allowed to jump to c1, c2, d3, e3, f3, or g1, if no capture was made, the king was not in check, and did not move over check. (The black king could move similarly.) In Lombardy, the white king could jump an additional square to b1 or h1 or to a2 (and equivalent squares for the black king). Later in Germany and Italy, the king move was combined with a pawn move.
In Rome from the early 17th century until the late 19th century, the rook could be placed on any square up to and including the king's square, and the king could be moved to any square on the other side of the rook. This was called "free castling".
In the Göttingen manuscript (ca. 1500) and a game published by Luis Ramirez de Lucena in 1498, castling consisted of two moves: first the rook and then the king.
The current version of castling was established in France in 1620 and England in 1640 .
Footnotes
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