Castling

Castling has its roots in the king's leap. There were two forms of the leap: the king would move once like a knight, or the king would move two squares on his first move. The knight move might 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 played 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 (Davidson 1981:48).

Before the bishop and queen acquired their current moves in the 16th century, their weak powers meant that the king was relatively safe in the middle of the board. When the bishop and queen got their current moves, they became very powerful, making the king 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 (Davidson 1981:16).

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[10] if no capture was made and the king was not in check and did not move over check. The black king might move similarly. In Lombardy, the white king might also jump to b1, h1, or a2, with equivalent squares applying to the black king. Later, in Germany and Italy, the king move was accompanied by a pawn move.

In the Göttingen manuscript (c. 1500) and a game published by Luis Ramírez de Lucena in 1498, castling consisted of moving the rook and then moving the king on separate moves.

The current version of castling was established in France in 1620 and in England in 1640 (Sunnucks 1970:66).

In Rome, from the early 17th century until the late 19th century, the rook might be placed on any square up to and including the king's square, and the king might be moved to any square on the other side of the rook. This was called free castling.

In the 1811 edition of his chess treatise, Johann Allgaier introduced the 0-0 notation. He differentiated between 0-0r (right) and 0-0l (left). The 0-0-0 notation for queenside castling was introduced in 1837 by Aaron Alexandre.[11] The practice was adopted in the first edition (1843) of the influential Handbuch des Schachspiels and soon became standard.

The rules of castling were amended in 1974 to remove a loophole that allowed for vertical castling with a newly promoted rook on the e-file, though this form of castling has only ever been known to be used in a few novelty chess problems.

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	a	b	c	d	e	f	g	h

White to play

Castling is generally an important goal in the opening because it serves two valuable purposes: it moves the king 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 regarding to which side one castles 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 can usually defend all of the pawns on the castled side. In queenside castling, the king is placed closer to the center, and the pawn on the a-file is undefended; for these reasons, the king is often subsequently moved to the b-file. In addition, queenside castling is initially obstructed by more pieces than kingside castling is; therefore, it may take slightly longer to achieve than kingside castling. On the other hand, queenside castling places the rook more efficiently on the central d-file, where it is often immediately active; meanwhile, with kingside castling, a tempo may be required to move the rook to a more effective square.

One may also forgo castling for various reasons. In positions where one's opponent cannot organize an attack on one's centralized king, castling may be unnecessary or even detrimental to king safety. In addition, a rook can be more active near the edges of the board than in the center in certain situations, such as if it is able to fight for control of an open or semi-open file.

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 (or opposite-side) 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 Yugoslav Attack in the Dragon Variation of the Sicilian Defence.

Under special circumstances, castling may also be a tactical idea. For example, in the diagram on the right, White wins a rook with 1.Qxd8+ Kxd8 2.0-0-0+ Ke7 3.Nxb5.[12]

• 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.[13] The arbiter answered in the affirmative, Korchnoi executed the move, and Karpov resigned shortly after.[14]
• Three castlings occurred in the game Wolfgang Heidenfeld–Nick Kerins, Dublin 1973. Of course, the third one (the second one by White) was illegal. The game is as follows:[15]

  1.e4 e6 2.d4 d5 3.Be3 Nf6 4.e5 Nfd7 5.f4 c5 6.c3 Nc6 7.Nf3 Qb6 8.Qd2 c4 9.Be2 Na5 10.0-0 f5 11.Ng5 Be7 12.g4 Bxg5 13.fxg5 Nf8 14.gxf5 exf5 15.Bf3 Be6 16.Qg2 0-0-0 17.Na3 Ng6 18.Qd2 f4 19.Bf2 Bh3 20.Rfb1 Bf5 21.Nc2 h6 22.gxh6 Rxh6 23.Nb4 Qe6 24.Qe2 Ne7 25.b3 Qg6+ 26.Kf1 Bxb1 27.bxc4 dxc4 28.Qb2 Bd3+ 29.Ke1 Be4 30.Qe2 Bxf3 31.Qxf3 Rxh2 32.d5 Qf5 33.0-0-0 Rh3 34.Qe2 Rxc3+ 35.Kb2 Rh3 36.d6 Nec6 37.Nxc6 Nxc6 38.e6 Qe5+ 39.Qxe5 Nxe5 40.d7+ Nxd7 0–1

• Tim Krabbé composed a joke chess problem containing vertical castling (king on e1, underpromoted rook on e8). The loophole in the definition of castling upon which this problem was based was removed by FIDE in June 1974 by the new requirement that the castling rook must occupy the same rank as the king.

Averbakh game

Averbakh vs. Purdy, 1960

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1									1
	a	b	c	d	e	f	g	h

Black to move castled queenside, with the rook going over the attacked b8-square.

In this game, Yuri Averbakh–Cecil Purdy (1960),[16] Black castled queenside. Averbakh pointed out that the rook passed over a square controlled by White, thinking this was illegal. Purdy pointed out that the castling was legal since this applies only to the king, to which Averbakh replied, "Only the king? Not the rook?" (Evans 1970:38–39), (Lombardy & Daniels 1975:188).

Edward Lasker game

Ed. Lasker vs. Thomas, 1912

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Position after 17...Kg1

In this game, Edward Lasker–Sir George Thomas (London 1912),[17] Black had just played 17...Kg1. White could have checkmated by 18.0-0-0#, but he instead played 18.Kd2#.[18] (See Edward Lasker's notable games.)

Prins versus Day

Prins vs. Day, 1968 (analysis)

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	a	b	c	d	e	f	g	h

Position before 31...0-0-0#

The diagrammed position is based on a hypothetical continuation of the game Lodewijk Prins–Lawrence Day (1968).[19] Black can checkmate by castling: 31...0-0-0#. (See Lawrence Day's notable chess games.)

Feuer versus O'Kelly

Feuer vs. O'Kelly, 1934

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Position after 12...Kxd8. White wins with 13.0-0-0+.

In the game Feuer–O'Kelly, Belgian Championship 1934,[20] Feuer perpetrated what later became known as a famous opening trap against O'Kelly when he castled queenside, simultaneously giving check and attacking O'Kelly's rook on b2, which had captured Feuer's pawn on that square.

Artificial castling (also called castling by hand)[21] is a maneuver in which a king which has lost the right to castle achieves a castled position in several normal moves instead of the one special move.[22]

Example

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Position after 5.Bxf7+?!

a b c d e f g h 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 a b c d e f g h Position after 9...Kg8

After the following common sequence of moves:

1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. Nc3 Nxe4 5. Bxf7+?! (first diagram)

White sees that if he recaptures with 5.Nxe4, Black responds with 5...d5, forking knight and bishop and winning back the piece. In that case, Black destroys White's center. Instead of allowing d5, White hopes to cause trouble for Black by returning the piece while depriving him of the right to castle. However, Black can easily castle artificially, for example:

5... Kxf7 6. Nxe4 Be7 7. 0-0

White castles "naturally".

7... Rf8

Black begins castling artificially.

8. d4 exd4 9. Nxd4 Kg8 (second diagram)

Black has achieved a normal castled position (Rf8, Kg8), but in several moves. The absence of any pawns in the center indicates that king safety is of particular importance in this position. Black's development lags slightly, but he also possesses the bishop pair and a queenside pawn majority, so his position is at least equal.

Variants of Western chess generally include castling in their rule sets, sometimes in a modified form.

In variants played on a standard 8×8 board, castling is often the same as in standard chess. A notable variant is chess960, which has modified castling rules to support different starting positions.

Castling can also be adapted to variants with different board sizes. Some such variants, like Capablanca Chess (10×8) or Chess on a Really Big Board (16×16), preserve the castling movement of the rooks, meaning it is the king that moves further along the board. Conversely, other games, like Dragonfly (7×7), specify that the king still castles two squares in each direction, and the rook is the piece that moves differently. A few variants, most notably Wildebeest chess (11×10), allow the player to choose how many squares they want to move the king (and move the rook accordingly).

There exist chess variants that do not have castling at all, such as losing chess. In variants played on non-rectangular (e.g. triangular, hexagonal, or three-dimensional) boards, castling usually does not feature.

Writing in 2019, former world chess champion Vladimir Kramnik proposed a variant of chess where players would not have the ability to castle. As the king could no longer castle into safety, this variant would theoretically lead to more dynamic games, as it would be considerably harder to force a draw and the pieces would be forced to engage in a mêlée.[23] In 2021, former world champion Viswanathan Anand defeated Kramnik in a no-castling exhibition match under classical time controls 2.5-1.5.[24]

Castling commonly features in chess problems. If the king and rook are on their original squares, castling is assumed to be legal unless it can be proved by retrograde analysis that either the king or the chosen rook has previously moved. Some retrograde analysis problems include a theme whereby one of the players (usually White) makes a move such as castling or an en passant capture in order to prove that the opponent has previously moved their king or rook and therefore cannot castle.

In most European languages, castling is known by a derivative from the same root as the English word "rook" (e.g. rochieren, rochada, enroque), while the local adjectives meaning "long" and "short" (or "big" and "small") are used in those countries to refer to queenside and kingside castling, respectively.

• Chess notation
  • Algebraic chess notation
  • Descriptive chess notation
• Outline of chess: Rules of chess
• Rules of chess
• Castle (shogi)

• Davidson, Henry (1981) [1949], A Short History of Chess, McKay, ISBN 978-0-679-14550-9
• Evans, Larry (1970), Chess Catechism, Simon and Schuster, ISBN 0-671-20491-2
• Hooper, David; Whyld, Kenneth (1992), "castling", The Oxford Companion to Chess (2nd ed.), Oxford University Press, ISBN 0-19-280049-3
• Just, Tim; Burg, Daniel B. (2003), U.S. Chess Federation's Official Rules of Chess (5th ed.), McKay, ISBN 0-8129-3559-4
• Lombardy, William; Daniels, David (1975), Chess Panorama, Chilton, ISBN 0-8019-6078-9
• Murray, H. J. R. (2012) [1913], A History of Chess, Skyhorse, ISBN 978-1-62087-062-4
• Schiller, Eric (2003), Official Rules of Chess (2nd ed.), Cardoza Publishing, ISBN 978-1-58042-092-1
• Sunnucks, Anne (1970), "castling", The Encyclopaedia of Chess, St. Martins Press, ISBN 978-0-7091-4697-1
• "Castling in Chess" by Edward Winter

• "Mate by Castling" Game Collection Chessgames.com