This paper examines Iron Age Mongolia during a time when nomadic tribes created the world's first steppe empire in Inner Asia. These aggregated tribes, known as Xiongnu (3rd century BC to the 2nd century AD), came to define steppe polity construction, later used by the Mongol Empire under the reign of Genghis Khan. They moved extensively over the eastern steppe and interacted, both in trade and intermarriage, with peoples from southern Siberia to Xinjiang. However, the Xiongnu as a people are relatively unknown to scholars, as they did not possess a written language. This study assesses Xiongnu population history and biological structure by analyzing craniofacial diversity via geometric morphometrics. Twenty-four coordinate cranial landmarks were used to test relationships among groups in the region and infer potential biological origins. The Relethford-Blangero R-matrix method was used to test hypotheses of phenotypic variation resulting from microevolutionary processes. This study hypothesizes biological continuity among Xiongnu individuals extending into modern Mongolian populations. Alternatively, long-range gene flow from adjacent geographic regions might suggest a complex