古備前

Ko-Bizen designates the swords produced in Bizen Province (southeastern modern Okayama Prefecture) during the Heian period, roughly the tenth through twelfth centuries, before the emergence of the Osafune school that would later dominate Japanese sword production. The geographic advantages of the Yoshii River valley—abundant magnetite sand iron for tamahagane steel, high-quality pine charcoal from the Kibi plateau, and direct waterway access to the Seto Inland Sea for distribution—gave Bizen smiths an unparalleled productive environment that they would exploit for the next six centuries.

The great Ko-Bizen masters—Tomonari, Kanehira, Sukehira, and Masatsune—produced tachi of extraordinary refinement, characterized by elegant slender proportions, deep koshi-zori curvature, small ko-kissaki tips, and restrained hamon patterns of ko-midare and ko-chōji rather than the flamboyant large chōji that later made Bizen famous. This aesthetic—influenced by Yamashiro court culture—reflects the Heian sensibility of mono no aware, a bittersweet aesthetic of transient beauty, translated into steel. Tomonari is considered the pinnacle of Ko-Bizen artistry; his surviving blades, designated National Treasures and Important Cultural Properties, show a close itame-mokume hamon with fine ji-nie that no later revival has fully reproduced.

The rise of warrior clans in the late Heian period—culminating in the Genpei War (1180–1185)—created new demand for tachi beyond the aristocracy, and Bizen smiths were already supplying eastern warriors before Kamakura period demand transformed their craft into mass production. By the early Kamakura period, the center of gravity had shifted downriver to Osafune, where Mitsutada established the Osafune school and began the transformation toward the bold, large chōji-midare hamon for which Bizen became internationally famous. Ko-Bizen blades survive in tiny numbers; genuine signed examples are museum treasures, and even unsigned attributions require the highest level of connoisseurship to authenticate.