《资治通鉴·梁纪·梁纪二》
北魏人用冲车撞城墙，所撞之处城墙上的土就掉下来一大片，昌义之用泥巴涂补，因此冲车虽然能撞入但不能撞毁城墙。
俄而堑满，冲车所撞，城土辄颓，义之用泥补之，冲车虽入而不能坏。
The Northern Wei people used a battering ram to hit the city wall, and a large section of the soil on the city wall fell off at the point of impact. Chang Yizhi applied mud to mend it, so the battering ram could smash into it but could not destroy the city wall.