This was a firm, long embankment that measured about four kilometers toward the southeast from Monzen Village, now around Ashimori Station of the JR West Kibi Line, to Kawazugahana, at the southern foot of Mt. Ishii, eight meters high, 24 meters deep, and 12 meters wide, designed to block the waters of Ashimori-gawa River.
この堤防は門前村（現：西日本旅客鉄道吉備線足守駅付近）から蛙ヶ鼻（石井山南麓）までの東南約4km、高さ8m、底部24m、上幅12mにわたる堅固な長堤を造り、足守川の水をせきとめようとするものであった。