O-O-O for queenside castling (with the letter O). ICCF numeric notation indicates castling based on the starting and ending squares of the king; thus, castling kingside is written as 5171 for White and 5878 for Black, and castling queenside is written as 5131 for White and 5838 for Black. History Castling has its roots in the king's leap. There were two forms of the leap: the king would move once like a knight, or the king would move two squares on its first move. The knight move might be used early in the game to get the king to safety or later in the game to escape a threat. This second form was played in Europe as early as the 13th century. In North Africa, the king was transferred to a safe square by a two-move procedure: the king moved to the player's second , and the rook and king moved to each other's original squares. Various forms of castling were developed due to the spread of rule sets during the 15th and 16th centuries which increased the power of the queen and bishop, allowing these pieces to attack from a distance and from both sides of the board, thus increasing the importance of king safety. The rule of castling has varied by location and time. In medieval England, Spain, and France, the white king was allowed to jump to c1, c2, d3, e3, f3, or g1 if no capture was made and the king was not in check and did not move over check; the black king might move analogously. In Lombardy, the white king might also jump to a2, b1, or h1, with corresponding squares applying to the black king. Later, in Germany and Italy, the rule was changed such that the king move was accompanied by a pawn move. In the Göttingen manuscript (c. 1500) and a game published by Luis Ramírez de Lucena in 1498, castling consisted of moving the rook and then moving the king on separate moves. The current version of castling was established in France in 1620 and in England in 1640. In Rome, from the early 17th century until the late 19th century, the rook might be placed on any square up to and including the king's square, and the king might be moved to any square on the other side of the rook. This was called free castling. In the 1811