[2] However, "Ki means "castle in the ancient language of Baekje, and was later simply assigned the kanji character for "demon.

In response, Emperor Tenji ordered the construction of a huge network of shore fortifications 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 (670–76), the Japanese would continue to build fortifications until 701, after finding out that Silla was no longer friendly with Tang.

[3] According to the Nihonshoki, twelve Korean-style mountain fortifications were built in western Japan at this time, and it is believed that Ki castle was one of them.

The identification of particular sites with the fortresses constructed at this time remains a subject of debate, and most fortifications of this period are classified under the wider term kōgoishi (神籠石).

Ki Castle is not mentioned in any historical documents, and the year of its construction is unknown, but archaeological excavations show that it was built in the latter half of the 7th century.

However, 1.5 meter wide paving stones are laid on the inside and outside of the bottom of the castle wall, giving it a strong atmosphere.

Relics related to Buddhism, such as tiled pagodas, water vases, and vessels, have been unearthed around the foundations of the buildings on the summit of the mountain.