In the game of chess, the pieces known as ROOKS are often referred to as castles. ROOKS are represented by a tower-like structure and are the most powerful pieces on the board. They can move horizontally or vertically across any number of squares. ROOKS are also used to protect other pieces on the board, such as the king and queen. The term 'castles' is often used to refer to ROOKS in chess because of their resemblance to a castle tower.