Japan's construction of defensive fortifications and its implications for East Asian relations during the Tang dynasty

Japan has constructed fortifications across centuries, from domestic embankments and stone works to overseas forts on the Korean peninsula. Challenging the common view that Japanese castle building needs arose only after the Battle of Baekgang (AD 663), this paper argues Japan perceived external tensions earlier. It examines defensive constructions at Itōjō and Ōnojo during the Tang dynasty and their implications for East Asian relations. Using historical records and archaeological evidence, the study proposes that Ōnojo’s construction may have begun around AD 650, predating Baekgang, and interprets these works as responses to evolving geopolitical pressures, particularly shifts in Japan–Silla–Tang relations. The analysis highlights how fortifications both reflected and shaped Japan’s diplomatic posture and internal centralization.

Zhuang Li, Kehua Liu