It location was designated a National Historic Site of Japan in 1979, with the area under protection expanded in 2007[2] In 660 AD, during the reign of Empress Saimei, the Korean kingdom of Baekje fell to an alliance of Silla and Tang China.

Crown Prince Naka no Ōe, later to become Emperor Tenji, and Empress Saimei decided to dispatch an expeditionary force to restore the Baekje kingdom, but this was decisively defeated by the Silla-Tang alliance at the Battle of Baekgang in 663 AD.

It was with this background that Emperor Tenchi decided to relocate the capital from Asuka to the shore of Lake Biwa in Ōmi Province.

In 1974, during rescue archaeology on the site of a new residential area in the Nishikiori neighborhood of Ōtsu, 13 pillar holes which are thought to have been the remnants of a monumental south-facing gate were discovered.

Further archaeological excavations have found Sue and Haji ware pottery, the presence of a double corridor extending from the South Gate to a large main hall, and the remnants of moats and earthen ramparts.