Castling is the only chess move in which the same player moves two pieces at the same time. It is a movement in which the king is involved in one of the player’s rooks. It is also the only move in which the king advances two squares and in which the rook can jump over another piece.
The movement consists of moving the king two squares or squares towards the rook in the first row of the player and, later, move the tower to the square over which the king has crossed.
There are two types of castling. On the one hand, there is the short castling (symbolized 0-0), in which the rook is situated on the king’s bishop square. On the other hand, there is the long castling (symbolized with 0-0-0), which is the one performed on the queenside.
To be able to make this play, a series of conditions must be met in the game, which are the following:
- That the king has never moved.
- That the rook to be used in castling has never moved.
- That the king is not in check.
- that none of the squares through which the king will pass or remain is under attack.
- Let the squares between the king and the rook be unoccupied.
- That the king does not end in check.
Although these conditions must be met, it must be taken into account that the chosen tower may be under attack. Further, in long castling, the square next to the rook can be attacked when castling is made and, also, the king could have been in check during the game, as long as he did not move to resolve the check
It should also be borne in mind that castling is impossible before the fourth move, since the knight and bishop have to be removed from the path, so a pawn move must be made. The player then has to think about whether it is worth castling or whether, on the contrary, it is better to take advantage of the play to develop another strategy or to protect the pieces from an attack.
In this video you can see both the play to make a short castling like a long castling: