Clothing refers to the cenotaph of Guo Pu, a writer in the Eastern Jin Dynasty. It is still in Xuanwu Lake Park in Nanjing. Chengguqiu refers to the cenotaph built by Jin Mingdi for Guo Pu, which was luxurious for a while. However, when the poets of the Tang Dynasty came to see it, it had become a ravine. Today it is called Guo Pudun, located in Xuanwu Lake Park in Nanjing.
You can refer to the History of Ancient Chinese Literature edited by Yuan Xingpei, Higher Education Press.