Castling

Once in every game, each king is allowed to make a special move, known as castling. Castling consists of moving the king two squares along the first rank toward a rook (which is on the player's first rank and then placing the rook on the last square the king has just crossed. Castling is permissible only if all of the following conditions hold

Neither of the pieces involved in castling may have been previously moved during the game.

There must be no pieces between the king and the rook.

The king may not be in check, nor may the king pass through squares that are under attack by enemy pieces, nor move to a square where it is in check.