The Âu Việt or Ouyue (Chinese: 甌越) were an ancient conglomeration of Baiyue tribes living in what is today the mountainous regions of northernmost Vietnam, western Guangdong, and northern Guangxi, China, since at least the third century BCE. They were believed to have belonged to the Tai-Kadai language group. In eastern China, the Ouyue established the Dong'ou or Eastern Ou kingdom. The Western Ou (西甌; pinyin: Xī Ōu; Tây meaning "western") were other Baiyue tribes, with short hair and tattoos, who blackened their teeth and are the ancestors of the modern upland Tai-speaking minority groups in Vietnam such as the Nùng and Tay, as well as the closely related Zhuang people of Guangxi.
The Âu Việt traded with the Lạc Việt, the inhabitants of the state of Văn Lang, located in the lowland plains to Âu Việt's south, in what is today the Red River Delta of northern Vietnam, until 258 or 257 BCE, when Thục Phán, the leader of an alliance of Âu Việt tribes, invaded Văn Lang and defeated the last Hùng king. He named the new nation "Âu Lạc", proclaiming himself "An Dương Vương" (literally "Peaceful Virile King"). The origins of Thục Phán are uncertain. According to traditional Vietnamese historiography, he was the prince or king of the Kingdom of Shu (in modern Sichuan). However the kingdom of Shu was conquered by the Qin in 316 BCE, making it chronologically improbable that Thục Phán was Shu royalty a hundred years later. There may be some merit to the story due to archaeological evidence of cultural ties between Yunnan and the Proto-Vietnamese, but possibly as a result of the gap in time between the origin of the story and when it was recorded, the location could have been changed to Shu or simply mistaken due to erroneous geographical knowledge. According to a translated oral account of a Tày legend, the western part of Âu Việt's land became the Nam Cương Kingdom, whose capital was located in what is today the Cao Bằng Province of Northeast Vietnam. It was there that Thục Phán hailed from. The authenticity of this account is considered suspect by some historians. It was published in 1963 as a translation while no extant copy of the original Tày text exists. The title of the story contains many Vietnamese words with slight tonal and spelling differences rather than Tai words. It is uncertain what text the translation originated from.
