Castling is a defensive supermove. It is the only occasion when you move two pieces and count it as one move. Castling involves the king and one of the rooks. The player may castle either to the left with the left rook, or to the right with the right rook.

Three conditions must be met to castle on the chess board:
• The king must not be in check.
• The king and the castling rook must not have been moved.
• The hex between them must be vacant and unthreatened.

Once the above conditions have been met, castle by moving the king next to the rook, then moving the rook to the opposite side of the king. (See below.)

before castling on the 3P3 chess board
Before castling on the chess board:
White and Black are ready to castle to their right. Red is ready to castle to Red's left.

castling on the 3P3 chess board
White, Black then Red castle on their turn.
1) The king moves next to the Rook.
2) The rook moves to the opposite side of the king.
(Black and White castle to their right; Red castles to Red's left).