Chess Castling: One of Your Best Defensive Weapons
Chess without castling could be likened to a boxing match with no gloves on. Without this well-designed safety measure, the game could get very dangerous very quickly - or otherwise could see each side tip-toeing around, sluggishly shifting their kings to safety.
Chess Castling allows both sides to swiftly retreat their king to a stronghold and rook toward the center in one convenient move. In the vast majority of games, both sides castle - but for the strategy to be effective, one must understand how best to wield castling with skill. Here, we’ll show you how.
What is Castling in Chess?
In a game of chess, castling is a special move where the king moves two squares toward a rook and the rook hops over to the square that the king passed over. Castling is the only move where you can move two pieces in the same turn!
Castling on the kingside is often referred to as short castling and castling on the queen’s side is called long castling. In its present incarnation, the rules of castling were finalized in the 1700s, primarily to make the game faster and more exciting.
The 5 Rules of Castling
There are some very peculiar rules around castling that are essential to know. Even grandmasters have been known to get confused about these, so even if you’re a chess veteran, you might learn something new!
1. You Can’t Castle if Your King or Rook Has Moved!
A player is forbidden to castle if either the king or rook that’s intended to castle has already moved during the game. This means there can be great advantage in forcing your opponent to move its king early on in the game!
2. You Can’t Castle Out of Check!
If your king is in check (directly threatened by an opponent’s piece), you’re not allowed to castle out of check.
3. You Can’t Castle Through Check (or into Check)!
As well as not being allowed to castle out of check, it’s also forbidden for the king to pass through or into a ‘checked square’ (a square directly attacked by an enemy piece).
4. You Can Only Castle Over Vacant Squares!
You can’t castle if any pieces (whether your own or an opponent’s) stand in between your king and rook. In other words, the squares in between must be vacant for castling to take place.
5. The King Must be Touched First!
In chess tournaments, and more serious friendly chess matches, there’s a rule often referred to as ‘touch-move’ – if you touch a piece, you must then move it. In the case of castling, you must touch the king first and complete castling with the same hand. If you touch the rook first, you must instead move the rook instead of castling!
The Key Benefits of Chess Castling
Moves the King to Safety
The primary function of castling is to move the king to safety. The center of the board is where all the action happens! The pawns in the center typically advance in the first few moves, leaving the king vulnerable to enemy attacks.
At sides of the board, however, pawns often remained unmoved, leaving a strong defensive wall to shield the back rank. By castling and moving the king behind the wall of pawns, the king is in the safest place on board.
Moves the Rook Toward the Center of the Board
Without castling, rooks (especially the kingside rook) can be awkward to centralize. The king stands in the way of the kingside rook reaching the e-file, and wouldn't be able to pass without the king first moving forward and then back again to safety. This would cost three moves instead of one!
By castling, the rook can easily reach the center of the board where it can bear more influence on the game. Indeed, early castling with a view to placing a rook on the e-file to x-ray the opponent’s king can be an extremely dangerous tactic, especially at beginner level!
Protects The Flank Pawns
An additional benefit of castling that’s sometimes forgotten is that the king does a tremendous job of protecting the flank pawns at the back of the board.
While we usually think of the pawns as protecting the king, the king returns the favor by protecting them too.
Castling and Defensive Structure
Chess Castling is primarily a defensive move. But for it to be effective, you’ll need to keep the king’s fort in good shape. Here are some basic principles to follow:
A Flat Pawn Structure is Usually Best
An extremely important aspect of castling is the pawn structure guarding the king. In general, the safest formation to shield your king is a flat pawn structure. (i.e. with all three pawns in front of the king unmoved).
Advanced Pawns on the a- and h-Files
There are some exceptions to the flat pawn structure rule. Pawns on the a- and h-files sometimes advance one square to defend against enemy pieces moving into attacking positions in front of your king.
The drawback of advancing pawns on the a- and h-files is that they are more easily challenged by enemy pawns or occasionally traded for a minor piece in a sacrificial assault on the king.
Opening the f-File
Advancing the f-Pawn and castling kingside is an aggressive yet risky strategy.
The advantage of advancing the f-pawn is that the kingside rook immediately attacks the vulnerable f-file upon castling. The disadvantage is that one of the three defending pawns has moved (and has often been sacrificed), leaving the king exposed.
While advancing the f-pawn is undoubtedly risky, the king can usually move into the corner of the board to avoid pesky checks. Just watch out for diagonal pins and skewers before you’ve had the chance to do so!
Fianchettoing the Bishop
A fianchettoed bishop is a bishop that's developed on the second rank of the b- or g-files. Normally fianchettoing happens after the b- or g-pawn has moved one square forward. In this formation, a fianchetto can form a strong structure to castle the king behind.
White has castled with an open f-file and is attacking f7.
A fianchettoed bishop acts as a sort of ‘super pawn’ that guards the entire central diagonal against enemy attacks. On the other hand, if the opponent's bishop of the same diagonal is still on the board, it can threaten an exchange with the defending bishop, which can leave a dangerous ‘hole’ in front of the king.
A Knight on f3 or f6 Holds the Fort!
Have you ever tried to attack an opponent’s fort, only to be fended off repeatedly by a knight on f3 or f6? A knight stationed on these squares (or c3 or c6 in queenside castling) often performs heroics in deterring enemy attacks.
In the image above, White’s knight of f3 is blocking ...Qxf2+. At the same time, it’s preventing the enemy queen from moving to either g5 or h4 where Black could attack from another angle. Last but not least, it's directly protecting h2 – one of the most vulnerable squares to a mating attack!
Watch Out for ‘Back-rank Mate’
Although castling behind a flat pawn structure usually offers the king the best defense, there is an exception to every rule!
Occasionally, the wall of pawns that usually defend the king so faithfully become his undoing by trapping him on the back rank. Known as a ‘back rank mate’, an opponent’s queen or rook hits the back rank and the king has nowhere to turn – a horrible way to lose the game!
During the end game, where a Back-rank checkmate could be a threat, it’s often worth advancing one of your king’s pawns to provide him an escape route. Choose carefully which pawn to advance! In the diagram above, White should advance its g-pawn, since h2 is being attacked by Black’s bishop.
When to Castle Short, When to Castle Long
In 80% of chess games, both sides castle. In 90% of castling instances, players castle kingside (short castling).
Why Short Castling (Kingside) is More Common
- Fewer pieces are standing between the king and the rook for castling to take place on the kingside (queenside castling requires the queen to be moved first).
- Short castling conveniently stations the king where it immediately defends all three flank pawns. Long castling moves the king two squares away from the a-pawn, meaning it often needs to move again to protect it.
- Many openings lend themselves to short castling. In the Queen’s Gambit, the English Opening, and the Sicilian Defense, for example, the c-pawn is advanced, prohibiting safe castling on the queenside.
When It's Better to Castle Long (Queenside)
- Castling long is a useful backup plan for when your kingside pawn structure has been weakened, when your kingside rook has moved, or when your opponent is already mounting a kingside attack.
- Castling on the opposite side of the board to an opponent is a popular strategy among players who like to deploy pawn storms. When flank pawns aren’t required to defend the king, they can instead be marched up the board to attack the enemy fort to great effect!
- Castling long immediately posts your rook on the d-file where it can bear great influence on the center. Occasionally, castling long can be used to dispatch a sudden pin, skewer, or dangerous check through the center.
When You Shouldn’t Castle at All
Occasionally it’s better not to castle at all. For instance:
- When both flanks are in poor order, yet the center is relatively strong, your king might remain safer in the center – especially if minor pieces are available to defend him.
- On rare occasions where queens and several pieces are exchanged very early in the game, it can be beneficial to have a centralized king, ready to become an active piece in the end game that ensues.
- When you’re launching a fast-paced attack on the enemy and can’t waste a move! In those instances, you need to use every move to deploy your attack as quickly as possible. If you’re lucky, you might win the game before castling is necessary!
Conclusions on Castling
Castling is a fundamental defensive strategy that helps the king to stay safe while centralizing a rook. In nine out of ten games, it’s a good idea to castle.
In the remaining 10 percent, where you either can’t castle or it’s better not to, you may well have difficulty defending your centralized king – thereby discovering why castling is so popular!
Experiment with castling on both sides of the board to see what works well for you. Castling on the opposite side to your opponent before launching a pawn storm can be an especially fun and effective tactic to overwhelm the enemy camp!