Ko-Tachi and Short Tachi: How Sword Length Reflected Japan's Changing Warfare

Defining the Terms

Ko-tachi (old tachi) typically refers to early curved swords of the Heian-early Kamakura period with blades around 60–70 cm. Kodachi (small tachi) denotes tachi-form swords under two shaku (approx. 60.6 cm), made for women's self-defense, aristocratic ceremony, or shrine dedication.

Heian Beginnings: Shorter Than Expected

The earliest curved tachi were considerably shorter than the Kamakura standard — 50–70 cm blades suited to mounted individual combat where maneuverability mattered more than reach.

Kamakura Standardization

The Kamakura period established the canonical tachi form: roughly 70–80 cm, deep koshi-zori (curvature near the base), tapering from broad moto-haba to narrower saki-haba. Small tachi continued to be made as shrine offerings and ceremonial blades.

Nanbokucho Paradox

While the era generally trended toward enormous odachi and nodachi, the practical utility of smaller swords ensured kodachi remained in daily use among foot soldiers and the general armed population who could not obtain or wield the massive battlefield blades.

Reading Length as History

Surviving blades roughly 60–65 cm suggest late Heian or early Kamakura production (or ceremonial use); 70–80 cm indicates Kamakura mainstream; over 90 cm points to Nanbokucho or early Muromachi. These are guidelines only — NBTHK appraisal is needed for definitive attribution.