Noin-Ula burial site
Many immigrants lived in the Xiongnu pasturelands, but at first they did not mix with the Xiongnu. To be a Xiongnu, one had to be a member of a clan, born of Xiongnu parents. The newcomers were well off, but were outsiders, and could marry only among themselves, not the Xiongnu. Only later did they intermix, increase in numbers, even created a state that existed from 318 to 350 AD.
History of Mongolia
The first significant appearance of nomads came late in the 3rd century BC, when the Chinese repelled an invasion of the Xiongnu (Hsiung-nu in Wade–Giles romanisation) across the Yellow River from the Gobi. A Chinese army, which had adopted Xiongnu military technology—wearing trousers and using mounted archers with stirrups—pursued the Xiongnu across the Gobi in a ruthless punitive expedition. Fortification walls built by various Chinese warring states were connected to make a 2,300-kilometre Great Wall along the northern border, as a barrier to further nomadic inroads.