《后汉书·列传·文苑列传上》
正值大司马吴汉逝世，光武诏令诸儒生为文吊唁，杜笃在狱中做了一篇诔文，辞旨高雅，光武称赞写得好，赐帛并免了他的处分。杜笃认为关中内山外河，是先帝的旧京，不应当改建洛邑，于是做了一篇《论都赋》，上奏皇上。
何则？物罔挹而不损，道无隆而不移，阳盛则运，阴满则亏，故存不忘亡，安不讳危，虽有仁义，犹设城池也。客以利器不可久虚，而国家亦不忘乎西都，何必去洛邑之渟瀯与？
It happened that the Grand Marshal Wu Han had just passed away, and Emperor Guangwu ordered all Confucian scholars to write funeral orations. In prison, Du Du wrote an eulogy in elegant language, which Emperor Guangwu praised and rewarded with silk and a pardon. Du Du believed that Guanzhong, with its mountains and rivers, was the former capital of the late emperor and should not be changed to Luoyang, so he wrote "On the Capital" and submitted it to the emperor.