The dō (胴) is the rigid torso protector worn in kendo, naginata, and related martial arts to shield the chest and abdomen during full-contact training. Its form is derived from historical samurai cuirasses, which were designed to protect vital organs while allowing freedom of movement in combat. As martial training became increasingly systematized during the Edo period, the dō was adapted from battlefield armor into a training implement suitable for repeated strikes. Traditionally constructed from lacquered bamboo slats bound together and later from leather or composite materials, the dō balances durability with flexibility, absorbing impact while preserving posture and mobility. Decorative lacquer finishes and regional design elements often reflect dojo identity and lineage. In practice, the dō serves not only as protective equipment but also as a reminder of the continuity between historical armor craftsmanship and modern martial discipline.