The History of Yuan Dynasty by Song Lian (Ming Dynasty)

In the Yuan Dynasty, China's maritime control was extended to the southern and central sections of the South China Sea. In 1279 (the sixteenth year of Zhiyuan), Kublai Khan ordered Guo Shoujing to preside over "the reconnaissance of the entire country." At that time, twenty-seven prospection sites were established throughout China. According to The History of Yuan Dynasty, the inspection "covered Goryeo (now the Korean peninsula) in the easternmost tip, the Dianchi Lake (now Yunnan Province) in the westernmost tip, Zhuya (now Hainan Province) in the southernmost point and Tiele (now Russian Siberia) in the northernmost point." According to research, the prospection point of in the South China Sea was established in the vicinity to the south of Xisha Qundao.