Complicating the frontier: Armaments, fortifications, and identities beyond the Great Wall

The recovery of iron and bronze “bimetallic” crossbow bolts from walled settlements located in the Mongolian Gobi Desert reflects the presence of Han dynasty material culture along the Inner Asian frontier during the Xiongnu period (ca. 3rd century BCE - 2nd century CE). Seventeen artifacts, mostly from frontier outposts, including eleven of these bimetallic projectile weapons and two bronze components of crossbows, were examined for their bronze chemical composition and microstructure. A majority of these artifacts were cast from alloys containing substantial amounts of tin and lead, with the alloy content generally much higher and more consistent in the bolts than in other crossbow components. The standard use of both tin and lead in most of these objects, as well as their process of assembly, suggest manufacture in an environment supporting large-scale, mass-production technologies typical of the Han dynasty. Some of the bolts examined, however, were made following significantly different alloy recipes, suggesting that they were likely produced away from well-supplied manufacturing centers. Given the clear limitations of the small number of objects analyzed, we combine our metallurgical results with insights from surface survey around these settlements to propose some preliminary observations about site arrangements, armaments, and supply lines. Although preliminary in nature, these differences hint at the complexities of politics and affiliation along the Inner Asian frontier.