In this study, Xu Songshi points out that there were various place names in southern China and extending into northern Vietnam which came from Zhuang, a Tai language. For instance, he states that there were many place names which began with the character “gu” (古), or “cổ” in Vietnamese, a term which he argues came from Zhuang and has been interpreted in many ways, from meaning “I,” to a classifier, to meaning a mountain with no vegetation on it. He also mentions that such place names could be found in the past from Anhui Province, in what is today central China, to Guangxi Province in the southwest, an area which he argues Tai speakers historically inhabited.9 Xu Songshi also cites a work which was published in 1877, Xu Yanxu’s Brief Compilation on Vietnam, which reportedly contains a map of the districts in Vietnam when it was under Chinese control in the early 15th century.10 This map apparently lists place names in what is today northern Vietnam such as the following: Cổ Bàng (古榜), Cổ Lão (古老), Cổ Lễ (古禮), Cổ Dũng (古勇), Cổ Long (古龍), Cổ Phí (古費), Cổ Đằng (古藤), Cổ Hồng (古宏), Cổ Lôi (古雷), Cổ Bình (古平), Cổ Đặng (古鄧), Cổ Xã (古社), and Cổ Nông (古農). Additionally, Xu Songshi states that characters such as tư/si (思), đô/du (都), đa/duo (多), na/na (那), bố/bu (布), and điều/diao (調) also represent Zhuang words, and that in Vietnam during the 15th century there were also place names with these characters, such as the following: Na Ngạn (那岸), Lục Na (陸那), Đa Cẩm (多錦), Đa Dực (多翌), Tư Dung (思容), Điều An (調安), and Bố Chân (布真).11 Unfortunately, Xu Songshi did not state what these other terms might have meant in Zhuang, although anyone familiar with a Tai language can tell that “na/na” is the term for a fi eld. While Xu Songshi therefore indicated that there was historically a strong Tai presence in the Red River Delta, he did not provide a clear historical explanation for how this happened.