Castling to me has always seemed like such a huge leap in terms of game play that I've always wondered how it came to be.
Does anyone know the history behind how and why castling came to be?
Castling was added to European chess in the 14th or 15th century and did not develop into its present form until the 17th century. The Asian versions of chess do not have such a move.
The King seems to have always moved the same as at the present, except that the game used to be played until he was actually captured. Because of the King's vulnerability due to the Queen's enormous scope and power, several methods of "castling" were tried before the 16th century.
One method was to allow the King to move two or three squares on its initial move. Another method was to allow the King to move directly to g2. The present method of castling was documented as early as Ruy López's 1561 work Libro de la invención liberal y arte del juego del Axedrez.
There seems to have been a rule in medieval chess, that does explain the invention of castling at least partly:
"The King's leap: for his first move, the King could jump at the 2nd square vertically, horizontally, diagonally or like a Knight. From e1 he could jump on c1, c2, c3, d3, e3, f3, g3, g2 ou g1. He could jump over an occupied square but not over a square under threat by an opposing piece. He could not capture with this leap nor jump to escape a check. However, he could still leap if he had been put in check on the previous moves."
Shatranj (and this variation of it) was a slow game and the king much less vulnerable then in today's chess (basically like a complicated endgame). So to speed it up, you could centralise your king in one move. When the queen and bishop suddenly got powerful, the king's leap was better used to hide your king away. Turning the rook move and the inevitably following king's leap into one move is very similar to turning the first two moves of a pawn into one double move.
So the introduction of castling was more evolution than revolution … ;-)