北宋末年，每当金兵南侵，宋朝统治者便关上城门，向士人征求意见；一旦金兵撤走，城门复开，统治者便禁止人们议论国事。这样“城门闭、言路开，城门开、言路闭。”反复几次后，北宋便灭亡了，连皇帝都成了金人的俘虏。后代史家总结北宋灭亡的原因时指出：北宋统治者平常... At the end of the Northern Song Dynasty, whenever the Jinbing southward invasion, the Song rulers shut the city gates and solicited opinions from the scholars. Once the Jinbing troops withdrew and the gates opened, the rulers forbade people from discussing state affairs. In this way “the city gates are closed, the words are open, the gates open, the words are closed.” After repeated several times, the Northern Song Dynasty will perish, and even the emperor became the prisoners of gold. Offspring historians conclude the reasons for the demise of the Northern Song Dynasty: North Song rulers usually ...