宋书
The name "Tatar" was first transliterated in "Book of Song" as 大檀 "Dàtán" (MC: *"daH-dan") and 檀檀 "Tántán" (MC: *"dan-dan") as other names of the Rourans, who were of Proto-Mongolic Donghu ancestry. The "Book of Song" and "Book of Liang" connected Rourans to the earlier Xiongnu while the "Book of Wei" traced the Rouran's origins back to the Donghu. Xu proposed that "the main body of the Rouran were of Xiongnu origin" and Rourans' descendants, namely Da Shiwei (aka Tatars), contained Turkic elements to a great extent. Even so, the Xiongnu's language is still unknown, and Chinese historians routinely ascribed Xiongnu origins to various nomadic groups, yet such ascriptions do not necessarily indicate the subjects' exact origins: for examples, Xiongnu ancestry was ascribed to Turkic-speaking Göktürks and Tiele as well as Para-Mongolic-speaking Kumo Xi and Khitans.