千葉氏
Byōbugaura was used as a defensive position overlooking the Pacific Ocean as early as the Kamakura period (1185–1333). Tsuneharu Kataoka (fl. 12th century), a grandson of the regional leader Taira no Tadatsune, used an area in front of the present-day location of Iioka Lighthouse on Cape Gyōbumi to build Sanuki Castle. Kataoka plotted against the first Kamakura "shōgun" Minamoto no Yoritomo, and Kataoka, his family, and local supporters were defeated and killed at Sanuki Castle by members of the Chiba clan. The remains of the castle have been lost out to sea due to marine erosion.