If you’re only just learning how to castle in chess, the four rules of castling are essential. Once you know the conditions under which a player is allowed to castle with the ♔ King and ♖ Rook, things get a whole lot easier.
Castling is a special chess rule where two pieces move at the same time. The king moves two horizontal spaces to the left or right, and the rook “jumps over” the king towards the opposite side of the king. Each player can only castle once per chess game.
While castling often happens in the early game, the special move not always allowed. Four specific preconditions should be met, before players are allowed to castle their king and rook. These are the four rules of castling in chess.
1. Both The King And Rook Haven’t Moved Yet
The first rule of castling states that the king and rook may not have moved for the whole game. For a castle move to be legal, a rook and king must remain in their starting positions on the board. A rook on either side of the board is allowed to castle (both kingside and queenside).
In other words, the very first move for the king and rook should be the castle move.
A player is not allowed to move the king, move back to the starting position (e1 for white, e8 for black), and then choose to castle. Following official chess rules, you can’t even touch a king or rook before castling. Remember this if you ever find yourself playing in a tournament.
This first rule also implies that a player is not allowed to castle more than one time per chess game.
2. The King Cannot Be In Check
Another important rule is the absence of immediate threats. A king in check is in no position to make a unique defensive chess move like castling. It must first remove the check threat in one of two ways:
- Move a supporting piece to remove the check threat (e.g. place a pawn on the attack line)
- Attack and take the check threat with a supporting piece (if possible)
A player intending to castle must always immediately protect their king from being in check. After the king comes out of check without moving, castling is allowed again. But don’t move your king to get out of check if you still want to castle! To keep your options open, always use a supporting piece to defend a king (or even defend a rook you intend to castle with).
Can’t manage to defend the king from a check threat with a supporting piece? Then a player is forced to immediately move the king out of check instead. After the king has moved, castling is no longer allowed because the first rule of castling is broken (see rule 1).
3. No Squares A King Moves Through Can Be Under Attack
Not only the king’s current position on the board must be protected against possible check threats. If you want to castle, both squares the king moves through must be safe as well.
That means that none of the opponent’s pieces can currently attack the squares relevant for castling.
To illustrate, take the threatening situation shown below. The ♛ Queen on h2 threatens the diagonal. Board position f1 is also under attack, and that’s a problem! A king that wants to castle has to remove the threat of the queen first, before castling is allowed to the right here (kingside):
4. No Pieces Can Stand Between The King And Rook
Also, note how castling to the left is not possible in the example shown before. There is a knight blocking the horizontal path between the ♖ Rook on a1 and the ♔ King on e1.
So what do we do here? Let’s make way for the royal king!
The fourth and last condition for castling states that no pieces are allowed to stand in between the king and rook. Not a single piece can block their movement, whether they are white or black pieces.
To clear the path for a castle move on the left side (i.e. queenside), we should move the ♘ Knight on b1 to board position c3 or d2. That’s a longer castle move between the rook on the left and the king. Assuming they haven’t moved yet for the whole game, of course.
Actually, ♘ Knight to c3 is the better play. It develops the knight a tiny bit better (and gives the rook the opportunity to defend line d later):
Advanced chess players like to think ahead a few moves, and give all their pieces a chance to develop on the board. We want to give them as many spaces to move to as possible. That’s how you gain a competitive advantage in chess.
Beginners should learn these four castling rules by heart. The four conditions for a castle move are set in stone, and will determine a lot of the strategy in the early part of the game. So if there is anything unclear about these four preconditions, don’t hesitate to ask a question in the discussion below this article. Talk to you there!
