Xiongnu
In the 1920s, Pyotr Kozlov's excavations of the royal tombs at the Noin-Ula burial site in northern Mongolia that date to around the first century CE provided a glimpse into the lost world of the Xiongnu. Other archaeological sites have been unearthed in Inner Mongolia and elsewhere; they represent the Neolithic and historical periods of the Xiongnu's history. Those included the Ordos culture, many of them had been identified as the Xiongnu cultures. The region was occupied predominantly by peoples showing Mongoloid features, known from their skeletal remains and artifacts. Portraits found in the Noin-Ula excavations demonstrate other cultural evidences and influences, showing that Chinese and Xiongnu art have influenced each other mutually. Some of these embroidered portraits in the Noin-Ula kurgans also depict the Xiongnu with long braided hair with wide ribbons, which is seen to be identical with the Ashina clan hair-style. Well-preserved bodies in Xiongnu and pre-Xiongnu tombs in the Mongolian Republic and southern Siberia show both Mongoloid and Caucasian features. Analysis of skeletal remains from sites attributed to the Xiongnu provides an identification of dolichocephalic Mongoloid, ethnically distinct from neighboring populations in present-day Mongolia. Russian and Chinese anthropological and craniofacial studies show that the Xiongnu were physically very heterogenous, with six different population clusters showing different degrees of Mongoloid and Caucasoid physical traits. These clusters point to significant cross-regional migrations (both east to west and west to east) that likely started in the Neolithic period and continued to the medieval Mongolian period.
Origin of the Huns
Other scholars have put forth evidence from non-European sources to support a link. Writing in third-century China, a Buddhist monk from northern Bactria (modern Afghanistan), named Zhu Fahu (in Chinese) or "Dharmarakṣa" (in Sanskrit), translated the ethnonym "Huṇa" from Sanskrit into Chinese as "Xiongnu". This is the earliest attested usage of the name Huṇa, and Étienne de la Vaissière argues that "the use of the name Huṇa in these texts has a precise political reference to the Xiongnu". A second important piece of textual evidence is the letter of a Sogdian merchant named Nanaivande, written in 313: the letter describes raids by the "Xwn" on cities in Northern China. Contemporary Chinese sources identify these same people as the Xiongnu. De la Vaissière, therefore, concludes that "'Hun/Xwm/Huṇa' were the exact transcriptions of the name that the Chinese [...] had rendered as 'Xiongnu'".
Another important historical document supporting the identification is the "Wei shu". Scholar Friedrich Hirth (1909) believed that a passage in the "Wei Shu" identified the Xiongnu as conquering the Alans and the Crimea, the first conquests of the European Huns. Otto Maenchen-Helfen was able to show that Hirth's identification of the people and land conquered as the Alans and the Crimea was untenable, however: the "Wei Shu" instead referred to a conquest of Sogdia by a group that Maenchen-Helfen identified with the Hephthalites, and much of the text was corrupted by later interpolations from other sources. De la Vaissière, however, notes that a Chinese encyclopedia known as the "Tongdian" preserves parts of the original "Wei Shu", including the passage discussed by Hirth and Maenchen-Helfen: he notes that it describes the conquest of Sogdia by the Xiongnu at around 367, the same time that Persian and Armenian sources describe the Persians fighting the Chionites. Sinor explicitly denied any connection between the Chionites and the Huns, claiming the former to have been Turks, unlike the Huns. However, writing in 2013, Hyun Jin Kim refers to a "general consensus among Historians that the Chionites and the Huns were one and the same". A fifth-century Chinese geographical work, the "Shi-san zhou ji" by Gan Yi, notes that the Alans and Sogdians were under different rulers (the European Huns and the Chionites respectively), suggesting some believed that they had been conquered by the same people.