mangue: The theories abound. Common one is that this rule was established in Edo period when it was ruled by feudal lords so in samurai code of ethics the pawn, the lowest rank in military, can not take the head of the lord. It was thought as rude and disgraceful. Another theory is that to make the game more interesting and fair for both players pawns' move need to have certain limits including ban of two pawns in one column. It is also said that this rule contributed the development of Tsume-shogi.