Miao was an old general term for Non-Chinese tribes, especially the southern tribes of the "four barbarians".
In high antiquity and mythological stories, the Three Miao Tribes (Sanmiao 三苗) are mentioned. They are also called "Miao people" (Miaomin 苗民), Youmiao 有苗, Miao family 苗氏, or Three Mao (Sanmao 三毛).
The scholar Liang Qichao 梁啟超 (1873-1929) proved that Miao was perhaps just another pronunciation of Man 蠻, another a designation for southern tribes (Nanman 南蠻).
The Sanmiao were according to legend part or descendants of the federation of the Nine Li Tribes (Jiuli 九黎), supporters of Chi You 蚩尤, the archenemy of the Yellow Emperor (Huang Di 黃帝). The geographical treatise Shanhaijing 山海經 explains that the Miao people were sons of Huantou 驩頭, who was in turn a son of Zhuan Xu 顓頊, one of the mythological five rulers. Some scholars hold that these "northern" Miao were different from the southern tribes.
The Three Miao were believed to have lived in the region of Hubei, Jiangxi and southern Anhui, at the banks of lakes Dongting 洞庭湖 and Pengli 彭蠡湖 (Lake Fanyang 鄱陽湖) and were the strongest among the barbarian tribes before the Xia period 夏 (21th - 17th cent. BCE). During the reign of the mythological emperor Yao 堯, they rose in rebellion, but were defeated by Yao in the battle of River Dan 丹水 (today called Danjiang 丹江, a tributary of the Yangtze in Hubei) and forced to accept Yao's suzerainty, but their rulers were acknowledged as "feudal lords" (zhuhou 諸侯). After further rebellions, Yao killed their chieftain and resettled them in the region of Mt. Sanwei 三危山 (in today's Gansu) or the southern wilderness. The then-reigning chieftain Huandou 驩兜 was banished to Mt. Chongshan 崇山 in the region of Cangwu 蒼梧 (close to today's Dayong 大庸, Hunan). When Yu the Great 大禹 founded the Xia dynasty, they rebelled one more and challenged the army of Yu in a battle which lasted for seventy days, but were finally defeated and enslaved.
It is known that the Miao used to prognosticate by weather and venerated their ancestors as well as natural spirites (shenling 神靈). The Miao also created fierce corporal punishments (wu nüe zhi xing 五虐之刑) and were thus seen as the inventors of penal law (see five punishments). Their society was divided into nobles (junzi 君子) and commoners (xiaoren 小人). One famous custon was to braid fibres into their hair (zhuashou 髽首).
In later ages, the ancient Miao merged either with Chinese, or with other barbarian tribes of the south. Some writers say, they were ancestors of the modern Miao 苗族 or Yao 瑤族 minorities, others even believe that the Qiang 羌 had ethnic relations to the Miao of high antiquity. The scholars Zhang Taiyan 章太炎 and Lü Simian 呂思勉 hold that the modern Miao have nothing to do with the ancient tribes.
The largest tribes during the Han period 漢 (206 BCE-220 CE) were Pangu 槃瓠, Linjun 廪君, and Banzhi 板櫍. The Pangu (also called Cong 賨) tribes were famous for their hemp clothes. The most important tribe of the Linjun were the Ba 巴 whose totem was a white tiger. The Banzhi were famous for their music and dances, but were also a martial people that often rebelled against the Han authority. Archeological artefacts give good impressions of the cultural autonomy of the old Non-Chinese tribes of Sichuan and Hunan.
During the rebellion of the Daoist Five-Pecks-of-Grain sect (Wudoumidao 五斗米道) under Zhang Lu 張魯 at the end of Eastern Han, many followers and believers were Non-Chinese Man people. After the downfall of Han and the disturbances during the Three Kingdoms 三國 (220~280 CE) and Western Jin 西晉 (265-316), Man tribes emigrated to the areas of modern Henan, Anhui, and Gansu, but their main settling region was still Hubei, Hunan, and Sichuan. The names of the tribes are manifold, like Jingyong-Man 荊雍蠻, Wuxi-Man 五谿蠻, or Dangyang-Man 當陽蠻, but it is uncertain if all these tribes represent an ethnic unity.
The empires in the area of Shu 蜀 (Sichuan), like Cheng-Han 成漢 (304-347), were characterized by a large Man population that had a partial political autonomy against the Chinese bureaucracy. The rulers of the Southern Dynasties 南朝 (420-589) and of the empires in Shu had always the problem that the Chinese farming population was not dense enough to support the economical and fiscal needs of the state and of the gentry. Many Man tribes were abducted form the hills and resettled in the plains as workforce for the Chinese state.
In the course of time, most of the Man tribes of the lower regions gradually merged with the Chinese population, but there are some ethnics (hilltribes) today thought to be descendants of the Man, like the Shezu 畬族 and Yaozu 瑤族.