Castling used to take 2 moves! Before our time, medival chess, the king could move two squares in any direction on the first move, and like a knight could pass over any player. This was when the queen and the bishops were really weak, and soon people realised that if you moved the rook next to the king and the the king to the corner, it would be safer, like castling, and it took two moves. Eventually, castling became 1 move as the bishop and queen grew stronger. (If any evidence is wrong please let me know)