Changes

Each player may castle only once during a game. Normally this is done during the first ten or fifteen moves.

If a pawn succeeds in marching all the way up the board to the far rank, it is given a special bonus. It is removed from the board and changed, as part of its last move, into a queen, rook, knight, or bishop at its owner's choice. This is called "promoting" a pawn. Since the queen is by far the most valuable of these pieces, a pawn is almost always promoted to a queen.