《资治通鉴·唐纪·唐纪四十五》
朱心中为长安感到忧虑，便加紧进攻奉天。他让僧人法坚制造云梯，长宽各有数丈，外面包裹着牛皮，下面安装着巨大的轮子，上面可以容纳勇士五百人，城中的人们望见，都感到忧恐畏惧。
泚内以长安为忧，乃急攻奉天，使僧法坚造云梯，高广各数丈，裹以兕革，下施巨轮，上容壮士五百人。城中望之忷惧。
Zhu was worried about Chang'an in his heart, so he intensified his attack on Fengtian. He asked the monk Fa Jian to make a siege ladder. It was several feet long and wide, covered in cowhide on the outside, and equipped with giant wheels on the bottom. It could accommodate five hundred warriors. When people in the city saw it, they were filled with fear and awe.