The Rare Book Preservation Society (文献保存同志会) was founded in 1940 by Zheng Zhenduo (郑振铎), Zhang Shouyong (张寿镛), He Bingsong (何炳松), Zhang Yuanji (张元济), and Zhang Fengju (张凤举) for the purpose of secretly acquiring and preserving rare books and manuscripts in the Shanghai Jiangnan region. These cultural assets have been accumulated by a number of famous private libraries some over 1,000 years.