Kon'ito Odoshi Yoroi: One of Japan's Three Great Armors

On the sacred island of Omishima in the Seto Inland Sea, the Oyamazumi Shrine (大山祇神社) safeguards one of the most remarkable collections of samurai arms and armor in all of Japan. Among its eight National Treasures, the Kon'ito Odoshi Yoroi (紺絲威鎧), or Blue-Laced Armor with Helmet and Large Shoulder Guards, stands as a masterwork of late Heian-period (12th century) craftsmanship. This magnificent ō-yoroi (great armor) is counted among the "Three Great Armors of Japan" (日本三大大鎧), alongside the Aka-ito Odoshi Yoroi at Musashi Mitake Shrine in Tokyo and the Kozakura-gawa Odoshi Yoroi at Sugata Tenjin Shrine in Yamanashi Prefecture.

According to shrine tradition, this armor was dedicated by the warrior Kōno Michinobu (河野通信), commander of the Mishima naval forces (三島水軍), as a votive offering of gratitude after fighting alongside Minamoto no Yoshitsune in the decisive Battle of Dan-no-ura in 1185, which brought victory to the Minamoto clan in the Genpei War. The armor has been preserved at this island shrine for over eight centuries, serving as a tangible link to the dramatic events that shaped medieval Japan.

What Is an Ō-Yoroi?

The ō-yoroi, or "great armor," was the signature protective equipment of elite mounted samurai during the Heian and Kamakura periods (roughly the 10th to 14th centuries). Designed primarily for horseback archery combat (騎射戦, kisha-sen), the ō-yoroi features a distinctive box-like silhouette that flares outward at the waist, providing both protection and freedom of movement for the warrior on horseback.

The construction of an ō-yoroi involves hundreds of small plates called kozane (小札), made from either iron or lacquered leather, laced together with colored cords in a technique known as odoshi (威). The color and material of the lacing cords give each armor its name: in the case of the Kon'ito Odoshi Yoroi, the lacing is done with deep indigo-blue (kon) hemp threads. The ō-yoroi was the highest-ranking form of samurai armor, sometimes called shiki-shō no yoroi, meaning "armor of proper ceremony." Only the most powerful warriors wore such armor into battle, making surviving examples extraordinarily precious.

Detailed Description and Artistic Features

The Kon'ito Odoshi Yoroi is a late Heian-period ō-yoroi of imposing presence, standing 76.0 cm in height. Its construction follows the classic ō-yoroi form while incorporating features that mark the refined aesthetic of the Fujiwara era.

The body of the armor (dō) is constructed from alternating plates of black-lacquered iron and leather kozane, laced together in the ke-biki (毛引) style using thick indigo-blue hemp cords. The ear cords (mimi-ito) are finished in a decorative takuboku (啄木, woodpecker) pattern, while the ridge lines (azemé) and diamond stitching (hishinui) are adorned with crimson monkey-skin leather (beni sarunumeshi). The cuirass features two tiers of standing plates (tateage) at the front, with the back consisting of three tiers including the push plate (oshitsuke), reverse plate (sakaita), and third plate. The hanging skirt (kusazuri) is divided into four sections (including the side shield, or waidate), with the front and back panels in four tiers and the left and right in five tiers.

The metal fittings (kanagu-mawari) and leather sections are covered with dyed leather featuring peony and arabesque motifs within diamond-cross circular patterns (tasuki-iri shishi botan en-mon some-gawa). These are edged with crimson leather borders and finished with indigo and white thread overlay, all framed with gilt-bronze rims. The decorative chemical plates (keshō-ita) are wrapped in iris-pattern leather (shōbu-gawa) with red and white end-pieces (habami), and fitted with silver-plated, openwork cherry blossom ornamental fittings (hassō kanamono).

The helmet (kabuto) is a riveted iron bowl (hoshi-kabuto) finished in iron-rust coloring, with prominent raised rivets (igaboshi) arranged in eleven rows of seven studs each, with three rows of five studs at the front center. The neck guard (shikoro) descends in five tiers in the cedar-standing (sugidate) form, with four tiers turning outward as blow-backs (fukikaeshi). The large shoulder guards (ōsode) consist of six tiers, with the drinking-cord rings (mizunomi-o no kan) attached on the inside.

Why Was It Designated a National Treasure?

The Kon'ito Odoshi Yoroi was designated a National Treasure on March 29, 1952, in recognition of several exceptional qualities. Although some portions were repaired in 1905 (Meiji 38), including sections of the lacing cords and the string-guard (tsurubashiri), the armor preserves its original form to a remarkable degree, clearly displaying the characteristics of late Heian-period armor construction.

Surviving examples of ō-yoroi from this era are extremely rare, and the use of hemp thread for the lacing (rather than silk) is a particularly noteworthy feature that distinguishes this armor from other examples. The hemp lacing is significant because it demonstrates an alternative material tradition in armor production that is seldom seen in extant pieces.

Furthermore, the armor's historical association with Kōno Michinobu and the Genpei War adds immense cultural significance. Kōno Michinobu was a prominent figure in the naval campaigns that decided the outcome of the war, and he is also notable as the grandfather of Ippen Shōnin (一遍上人), the founder of the Ji-shū sect of Buddhism. This combination of artistic excellence, rarity, historical importance, and exceptional preservation makes the Kon'ito Odoshi Yoroi an irreplaceable cultural asset.

Kōno Michinobu and the Battle of Dan-no-ura

Kōno Michinobu (河野通信, dates uncertain) was the commander of the Mishima naval forces based in Iyo Province (present-day Ehime Prefecture). During the Genpei War (1180–1185), the conflict between the Taira (Heike) and Minamoto (Genji) clans for control of Japan, Kōno Michinobu sided with the Minamoto forces under Yoshitsune.

The Battle of Dan-no-ura (1185), fought in the narrow strait between Honshū and Kyūshū, was the final and decisive naval engagement of the Genpei War. The Kōno naval fleet played a crucial role in the Minamoto victory. According to tradition, Kōno Michinobu dedicated this armor to Oyamazumi Shrine as a gesture of thanksgiving for the divine protection that led to this triumph. Oyamazumi Shrine, dedicated to the god of mountains, sea, and warfare, had long been the spiritual guardian of the warriors of Iyo, making it the natural recipient of such a significant votive offering.

Oyamazumi Shrine: Japan's Greatest Armor Treasury

Oyamazumi Shrine is not merely the home of the Kon'ito Odoshi Yoroi — it is the single greatest repository of historic armor in Japan. The shrine holds approximately 40 percent of all armor and weaponry in the nation that has been designated as National Treasures or Important Cultural Properties. In total, the shrine possesses 8 National Treasures and 76 Important Cultural Properties, earning Omishima the nickname "Island of National Treasures" (国宝の島).

The shrine's remarkable collection is a result of centuries of devotion by warriors and naval commanders. As the head shrine of all Oyamazumi and Mishima shrines across Japan, it enshrined Ōyamatsumi-no-kami (大山積神), a deity revered as the god of mountains, the sea, and military fortune. From the aristocrats and warriors of the Heian period through the naval forces of the Seto Inland Sea, generations of fighting men entrusted their most prized possessions — their weapons and armor — to the care of this sacred site.

In addition to the Kon'ito Odoshi Yoroi, the shrine's National Treasure armors include the Aka-ito Odoshi Yoroi (traditionally attributed to Minamoto no Yoshitsune), the Murasaki-aya Odoshi Yoroi (attributed to Minamoto no Yoritomo), and the Omodaka Odoshi Yoroi (the oldest surviving example of a Japanese ō-yoroi). Other National Treasures in the collection include two magnificent great swords (ōdachi), an exquisite sword-mounting with peony-arabesque chain fittings, and a Tang-dynasty bronze mirror with animal and grape motifs.

Visiting the Treasure Hall

All eight of Oyamazumi Shrine's National Treasures are normally on permanent display in the shrine's Treasure Hall (宝物館), which comprises the Kokuho-kan (National Treasure Hall) and the Shiyō-den (紫陽殿). Visitors can view these priceless artifacts during regular opening hours. Photography is not permitted inside the exhibition halls.

The Treasure Hall was originally established in 1926 (Taishō 15) and later expanded with the addition of the Shiyō-den in 1962 (Shōwa 37). The buildings themselves are of architectural interest: the original hall features a reinforced-concrete design with Shinto-inspired decorative elements. Together, the halls house tens of thousands of artifacts spanning more than a millennium of Japanese history.

A combined admission ticket also grants access to the Omishima Maritime Museum (大三島海事博物館), which displays the research vessel Hayama-maru used by Emperor Shōwa (Hirohito) in his marine biology studies, along with documents related to the Murakami naval forces (村上水軍) of the Seto Inland Sea. Allow approximately one hour for a thorough visit to both facilities.

Surrounding Attractions

Omishima Island and the Shimanami Kaido cycling route offer a wealth of experiences beyond the shrine. The shrine grounds themselves are home to ancient camphor trees (楠), 38 of which are designated as a national Natural Monument, creating a serene forest atmosphere. Near the main hall, the "Living Tree Gate" (生樹の御門), a giant camphor tree with a natural tunnel through its trunk, leads to the shrine's inner sanctuary (Oku-no-in).

The Shimanami Kaido, the network of bridges and cycling paths connecting Honshū to Shikoku across the islands of the Seto Inland Sea, is one of Japan's premier cycling destinations. Omishima sits at the heart of this route, making it easy to combine a cultural visit with an active outdoor experience. Nearby, the Michi-no-Eki Shimanami no Eki Mishima roadside station offers local products and refreshments, while the Maré Grassia Omishima facility provides seawater bathing with panoramic ocean views.

For those interested in further historical exploration, the Murakami Kaizoku Museum (村上海賊ミュージアム) on neighboring Oshima Island documents the history of the Murakami naval clans who dominated these waters during the medieval period. Dōgo Onsen, one of Japan's oldest hot spring resorts, is accessible from Imabari and makes an excellent addition to an itinerary that includes Omishima.