Castling in Chess
Castling is a common occurrence in chess. Games can be won and lost on the player’s ability to castle at certain points in the game. The basics of castling are that the king and one of the rooks cross over in a single move. The king moves two squares and the rook ‘jumps’ over him, landing on the square on the other side. Let’s have a look at some of the conditions under which castling is or is not allowed.
Pre-requisites
Clear the way
First of all, all the pieces between the rook and the king must be out of the way in order for castling to take place. If you’re castling on the queen’s side, this means the queen too has to move up from the back rank where she started. On the king’s side, it could look something like the following scenario:
Here, the king-side knight has advanced to f3 and the pawn in the e file has advanced one square to let out the king-side bishop, which has then advanced to d3. The order of the first 3 moves is unimportant. The pawn can move first, but so can the knight, the crucial thing is that both the bishop and the knight move before the castling can take place.
First move for both king and rook
Not only must the other pieces have moved out of the way, but it’s also crucial that neither the rook you’re castling with or the king himself have not moved before castling. This means, once your king moves, castling is not possible at all. If one rook moves, then castling on that side is no longer possible, but castling on the opposite side may still be possible if the opposite rook has not yet moved.
No checks
Next, it’s not possible to castle out of or through check. This means that if your opponent has you in check, you may not castle on that turn. Of course, if you must or choose to move your king to avoid check, then, according to the previous rule, castling will no longer be possible afterwards. However, if you successfully block the check with another pieces, or take your opponent’s piece causing check, then castling will still be possible at a later time.
Here is a scenario where it would not be possible to castle on this turn:
Here the bishop on b4 is checking the white king and therefore preventing white from castling. In this scenario, white would likely block the bishop, using any of the following moves:
Most obviously by pushing the pawn on c2 up to c3. This would aleviate the check on the king and would also put pressure on black to move the bishop for fear of it being taken by the pawn. Alternatively, the knight on b1 could move to either c3 or d2 to block the bishop, or the white bishop on c1 could move to d2. Queen to d2 would be possible in theory, but the black bishop would then be able to take the queen, which would be a huge loss for white.
This rule also applies for castling through checks, which can often be a problem. This means that if your king would travel through a square that is being attacked by an opponent’s piece - most commonly a bishop, but it can be any piece - then you cannot castle at that point. First, you will have to block, capture, or force away the opponent piece that is preventing the castling before proceeding to castle. Let’s have a look at an example of such a scenario.
In this scenario, white has successfully cleared the way for king-side castling by moving the king-side knight up to f3 and the king-side bishop has been what’s known as fianchettoed, and is out of the way of the king and the rook. However, black has moved the queen-side bishop to a6, which is now attacking all the way along the diagonal down to f1, a square which the white king would move through if white were to castle at this point. Due to this, white cannot currently castle as that would involve the king moving through check, which is not permitted. If white still wishes to castle from this point, the black bishop needs to be blocked, captured, or otherwise forced away from its position. Doing so could require several moves in this case, and this could give black an advantage in the game.
Bear in mind that the squares that the rook will travel through while castling can be under attack from the opponent’s pieces and castling is still allowed, this includes the rook’s starting position. Consider this example:
This time the black queen-side bishop has fianchettoed on b7 and is attacking the long diagonal down to white’s king-side rook on h1. In this position white can still castle, since the king would not be travelling through check or ending up in check.
Castling strategy
It’s often considered a good idea to try to castle in a game of chess. While there are no universal rules, it can be a real weakness if your king stays in the centre of file. Tucking him away and out of harm’s way is a good way to keep him safe. Bear in mind that there are many players who excel in attacking a castled king, since castling puts the king in a corner which can be used to trap him, espcially with many pieces around him to hamper any escape routes.
Castling on opposite sides
It’s most common for players to castle king side. If both players do this in a game, then both are in similar, but symmetrical positions. This means that although there are still techniques to break open the castled position, these are more advanced and can easily fail. One common pattern, however is when you and your opponent have castled on opposite sides - one to the king-side and the other to the queen-side. In this scenario, most players choose to deploy a so-called pawn storm on their opponent’s king. This means that you take the pawns on the side where you haven’t castled, and advanced them up to break through your opponent where they have castled. Since the benefit of castling is putting the king nicely tucked away behind his pawns, attacking that with your own pawns can be an effective way of breaking down that defence and opening the position up.
If you have any comments, feedback or questions about anything in this post, leave them below.