ABSTRACT
The Beibu Gulf, also the Gulf of Tonkin, is a body of water partially enclosed by northern Vietnam, southern China and China’s Hainan Island. With an average water depth of 38 meters (the deepest water being less than 90 meters) and a flat seabed, the gulf encompasses an area of about 44,238 square kilometers (24,000 square nautical miles). The signing of the Sino-French Treaty of Tientsin on June 9, 1885, paved the way for the border demarcation between China and France. Geographically, Tonkin shares a border with three of China’s southwestern provinces: Guangdong, Guangxi and Yunnan. As the border area is crisscrossed by mountains and rivers, it is difficult to identify the boundaries. As Taiwanese historian Guo Tingyi notes: Some people who have crossed the Sino-Vietnamese border, after trekking several kilometers in Vietnam, found themselves again on the territory of the Qing Dynasty.
