During the excavation and research of the "Mt. Otsubo" kogo-ishi in Takeo City in Saga Prefecture in 1963, the dorui (earthwork) built using the "hanchiku" construction method behind the arranged stones, and the traces of posts aligned at three-meter intervals in front of the arranged stones were discovered, and as a result it was widely accepted that kogo-ishi were mountain castles.
昭和38年（1963年）の佐賀県武雄市「おつぼ山」神籠石の発掘調査で、列石の背後にある版築によって築かれた土塁と、列石の前面に3m間隔で並ぶ堀立柱の痕跡が発見され、山城であることが確定的となった。