In contrast to the beginnings of classical Chinese medicine in the Han period, our knowledge of early medieval medicine is still sketchy. This is due largely to a lack of sources. Of the more than 100 medical texts recorded in the Old Tang History (Jiùtángshū 《舊唐書》, 945 CE), only four have survived in the received literature from the early medieval period: Cháo Yúanfāng’s 巢元方 Zhūbìng yuánhòu lùn 《諸病源候論》 (On the Origins and Symptoms of the Various Diseases, 610 CE), Sūn Sīmiǎo's 孫思邈 Bèijí qiānjīn yào fāng 備急千金要方 (Essential Formulas worth a Thousand in Gold for Every Emergency, 652 CE, in the following discussion abbreviated as Qiānjīnfāng), his Qiānjīn yìfāng 千金翼方 (Supplementary Formulas worth a Thousand in Gold, 682 CE), and Wáng Xī’s Wàitái mìyào 外台秘藥 (Essential Secrets From the Palace Library, 752). Other texts are known only from quotations in compendiums like the Japanese Ishimpō 醫心方 (Prescriptions from the Heart of Medicine, 984 CE), a collection of early medieval Chinese medical literature by a Japanese court acupuncturist. The other great source for medical literature from this period is the corpus of medical manuscripts found in Dūnhuáng 敦煌, which date mostly to the Suí and early Táng periods.