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.

The outer wall of earthworks and stone embankments, which runs from the horseshoe-shaped ridge around the mountaintop to the valley, is approximately 6.8 kilometers long.

[4] Per the Nihon Shoki, the castle was built in fourth year of the reign of Emperor Tenchi, or 665 AD, with construction carried out largely by exiles from Baekje.

[4] In July 2003, unusually heavy rains caused landslides, and over a period of six years starting in 2004, restoration work related to the ruins was carried out at approximately 30 locations.