How to Castle

Once during the game, the King can make a special move.

Castling is the only situation where you can move two pieces at the same time. The pieces are always the King and one of the Rooks. Of the several restrictions on castling, the first is that the King and the Rook to be moved are on their initial squares and haven't moved. The diagram shows the ideal case for both Kings and all four Rooks. How do you know the Kings and Rooks haven't moved and then moved back to their initial squares? If you're playing a game with someone else, you have to remember. Sometimes beginning players forget -- 'You already moved that Rook'! 'No, I didn't'! 'Yes, you did'! 'Prove it'! -- In this diagram, you have to take my word for it. The second restriction is that the squares between the King and the Rook must be empty. Since the other pieces have all disappeared in the diagram, the condition for castling is met.

Castling is executed by moving the King two squares toward the Rook, then hopping the Rook over the King. The diagram shows how the pieces end up after castling in the previous diagram. First White has castled to the right. Then Black castled to the right.

This diagram shows the board after both players have castled to the left. There is, of course, no rule that both players have to castle on the same side. Sometimes one player castles to the left and the other castles to the right. This is known as 'castling on opposite sides' of the board.

In this diagram both players have lost the right to castle. White can't castle, because the King has already moved. Black can't castle because both Rooks have already moved.

There are other restrictions on castling. You can't castle if your King is under attack. In this diagram, the white Bishop is attacking the black King, so Black can't castle to either side.

You also can't castle if your King moves through a square that is under attack. In this diagram, the white Bishop is attacking the square to the left of the black King, so Black can't castle in that direction. Black can, of course, still castle to the right.

You also can't castle if your King ends up on a square that is under attack. In this diagram, the white Bishop is attacking two squares to the left of the black King, so Black can't castle that way. Once again, Black can castle to the right.

There are two rare situations which are not restricted by the rules. There's no problem if the Rook is under attack just before you castle. It can't be under attack after you castle, because that would mean the King just moved through an attacked square. If you castle to the left, it also doesn't matter if the Rook moves through a square that is under attack. In this diagram, White can castle to the left or to the right.