In response, a huge network of shore fortifications was constructed throughout the rest of the 600s, often with the assistance of Baekje engineers, generals and artisans.

Unaware of the outbreak of the Silla-Tang War (670–676), the Japanese would continue to build fortifications until 701, even after finding out that Silla was no longer friendly with Tang.

[4] Kiyama Castle is located approximately eight kilometers south of the Dazaifu Government Office ruins, overlooking the branch point of the ancient government highway connecting Dazaifu with Higo Province and Chikugo Province.

From the castle it is possible to see Hakata Bay to the north, and the Ariake Sea to the east, with the Serifu Mountains to the west.

An entry dated 698 in the Shoku Nihongi mentions repair work undertaken at Kii Castle.