The bulwark against Mongolian invasion was built with a financial support from the lord of Buzen province in Edo period, along the beach stretching from Nagatare Mountain to Imayama Mountain. Today, the bulwark in front of Nagatare Beach and the one at the bottom of Imayama Mountain are government-designated ruins. According to a historical report in an ancient document, Narutomi clan, the local clan of Edo period based in Yoshitomi-mura village of Chikujo-gun, was in charge of the construction of the bulwark and completed it in 1303. It suggests that the construction was continued for a long time and the nation was kept under a warned status against Mongolians even after the Koan Invasion of 1281.