Book of Zhou
An early form of the same name may be reflected in the form of "tie-le" (鐵勒) or "tu-jue" (突厥), name given by the Chinese to the people living south of the Altay Mountains of Central Asia as early as 177 BC. The Chinese Book of Zhou (7th century) presents an etymology of the name "Turk" as derived from "helmet", explaining that this name comes from the shape of a mountain where they worked in the Altai Mountains.