By the middle of the Northern Song dynasty, formerly upright pieces became uniformly flat; the pieces no longer moved from square to square, but along the lines from intersection to intersection; a boundary river was added to the center of the chess board; and on each side the field marshal was confined to a square "palace of nine halls" (so-called since a square encompasses nine points where lines intersect).
北宋中葉，象棋最基本的形制﹘ ﹘立體棋子，一轉而為平面棋，棋子則越出格子，走線與線間的交叉點，棋盤並出現河界與九宮（將帥被限制的四方格）。