From the 2nd century BC to the 2nd century AD, the Han Dynasty (East Asian agricultural civilization) and the Roman Empire (Mediterranean maritime commercial civilization) rose at Eurasia’s two ends. To resist harassment from northern nomadic tribes like the Xiongnu, the Han established an inward-looking border defense system centered on the Great Wall. In contrast, the Roman Empire built an outward-looking system based on professional legions to address multi-front threats. This paper compares their core characteristics, analyzes the geographical, economic and political causes of differences, summarizes historical experiences, and provides reference for contemporary border governance.