Ken (Unsigned): A Straight, Double-Edged Sword from Heian Japan
Most famous Japanese blades curve. This one does not. The unsigned ken owned by Amanosan Kongo-ji temple runs dead straight for 62.3 centimeters, sharpened along both edges, with a ridgeline rising on each face of the blade. In the vocabulary of Japanese sword scholarship this construction is called ryo-shinogi-zukuri, and surviving examples of any quality are scarce. The Agency for Cultural Affairs, which designated the sword a National Treasure on March 31, 1953, calls it the finest old ken of all in both form and forging.
The word ken (also read tsurugi) refers to this older, symmetrical type of sword, a form that reached Japan from the Asian continent centuries before the curved tachi and katana were developed. By the Heian period (794 to 1185), when this blade was forged, the ken had largely left the battlefield. It survived instead as a ritual object of esoteric Buddhism, the weapon held by Fudo Myoo, the wrathful guardian deity whose sword cuts through delusion.
That is precisely the context this sword comes from. Kongo-ji, a Shingon temple in the hills of Kawachinagano in southern Osaka Prefecture, records in its tradition that the blade belonged to Akan, the monk credited with rebuilding the temple in the late twelfth century, and that he used it in religious ceremonies. The attribution cannot be verified, and the official record is careful to present it as temple lore rather than fact. What the steel itself shows, however, places the work firmly in the Heian period.
Why It Was Designated a National Treasure
The sword first received national protection in 1937, when it was named an Important Cultural Property. Its elevation to National Treasure came in 1953, under designation number 00107 in the crafts category.
Two qualities drove the decision. The first is rarity of type: straight, double-edged, double-ridged blades from this era barely exist. The second is the evidence of age written into the metal. The hamon, the crystalline temper line along the cutting edge, stops well short of the hilt in a feature called yakiotoshi, a habit of early swordsmiths that faded from practice after the Heian period. Combined with the character of the steel surface, this allowed appraisers to conclude the blade can be no later than Heian work.
The designation also covers an accessory: a black-lacquered ceremonial mounting known as the kokushitsu hoken koshirae. Its gilt hilt is shaped as a sanko, the three-pronged vajra implement of esoteric ritual, so that the mounted sword takes the very form carried by Fudo Myoo in Buddhist painting and sculpture. Sources differ on the mounting's age. The temple describes it as Heian work, while a 2022 exhibition at the Kyoto National Museum dated it to the thirteenth century, in the Kamakura period. Either way, blade and mounting together preserve a complete image of the esoteric ritual sword.
Reading the Blade
Stand in front of the case and start with the silhouette. No curvature at all. The two edges taper evenly toward the point, and a low ridge runs down the center of each face, catching the light differently as you shift your viewing angle.
Then move closer. The forging grain, called jihada, is itame, a wood-grain pattern mixed with swirling mokume figures. Bright particles of ji-nie scatter across the surface, threaded with dark linear features known as chikei and patches of jifu. Heian steel has a wet, layered depth that later, more uniform forging rarely matches, and this blade is a textbook place to see it.
The temper line rewards patience. It is a narrow suguha, a straight line, but broken by small irregularities called ko-midare, with a soft, slightly hazy nioiguchi boundary and fine ko-nie crystals. In places the hardening visibly thins out or breaks. The tip pattern, or boshi, turns back in a small circle. None of this is showy. Heian sword aesthetics prized restraint, and the appeal here is quiet rather than dramatic.
The tang remains ubu, meaning never shortened, with a chestnut-shaped end, file marks slanting gently downward, a single peg hole, and no inscription. The notches where blade meets tang are cut in an unusual two-step profile. For sword students, an unaltered Heian tang is a document in itself.
Where to See It, and the Temple Behind It
The sword does not live at Kongo-ji. It is on long-term deposit at the Kyoto National Museum in Higashiyama, Kyoto, and it is not part of any permanent display. It appears periodically in the museum's collection galleries and in special exhibitions; recent outings include the 2017 National Treasures exhibition, the 2019 deposited-masterpieces show, a 2022 exhibition on Kanshin-ji and Kongo-ji, and a collection gallery rotation in 2023. Anyone hoping to see it should check the museum's exhibition schedule in advance rather than making a special trip on chance. The museum is a short walk from Shichijo Station on the Keihan Line, and photography rules vary by gallery, so follow the posted signage.
The temple that owns it deserves a journey of its own. Amanosan Kongo-ji sits in a wooded valley in Kawachinagano, about an hour south of central Osaka. Tradition holds that the monk Gyoki founded it in the Nara period and that Kukai, founder of Shingon Buddhism, once trained on the site. The documented turning point came in the late 1100s, when Akan restored the halls with the backing of Retired Emperor Go-Shirakawa and his sister Hachijo-in. Because women could worship here at a time when Mount Koya barred them, and because women of Hachijo-in's court served as head of the temple for four successive generations, Kongo-ji earned the name Nyonin Koya, the Women's Koya.
The grounds repay slow walking. The Kondo main hall, an Important Cultural Property, houses a colossal seated trio of Dainichi Nyorai, Fudo Myoo, and Gozanze Myoo, designated National Treasures in 2017. A vermilion two-storied pagoda dates in origin to the twelfth century. In the fourteenth century the temple served the Southern Court as a temporary imperial seat, and the room arrangement of those years can still be traced. To reach it, take the Nankai Koya Line to Kawachinagano Station, then a Nankai bus on the Amanosan route to the Amanosan stop in front of the gate.
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Q&A
- Can I see this sword if I visit Kongo-ji temple?
- No. The sword is deposited at the Kyoto National Museum and is not shown at the temple, even during its treasure exhibitions. It goes on view only when the museum includes it in a collection gallery rotation or special exhibition, so check the museum's schedule before planning a visit.
- How is a ken different from a katana?
- A ken is straight and sharpened on both edges, an older form that came to Japan from the continent. The katana and its predecessor the tachi are curved and single-edged. By the Heian period the ken was used mainly in Buddhist ritual rather than combat, which is why this example survived in a temple.
- Why would a Buddhist temple own a sword at all?
- In Shingon esoteric Buddhism the sword is an attribute of Fudo Myoo, symbolizing the cutting away of ignorance. Temple tradition says this blade was the personal ritual implement of Akan, the twelfth-century restorer of Kongo-ji, and its mounting with a vajra-shaped hilt reproduces the deity's sword exactly.
- Is Kongo-ji itself worth visiting even though the sword is in Kyoto?
- Yes. The temple holds other National Treasures, including the monumental seated triad in its main hall, along with a historic garden, a twelfth-century pagoda, and the history of the Nyonin Koya, where women could worship when Mount Koya excluded them. It is about ninety minutes from Osaka by train and bus.
Basic Information
| Name | Ken (Unsigned) / 剣〈無銘〉 |
|---|---|
| Category | National Treasure (crafts), designation no. 00107 |
| Designation dates | Important Cultural Property: May 25, 1937 / National Treasure: March 31, 1953 |
| Quantity | 1 blade, with attached black-lacquered ceremonial mounting (kokushitsu hoken koshirae) |
| Period | Heian period |
| Dimensions | Blade length 62.3 cm, width at base 3.3 cm, tang length 11.1 cm |
| Owner | Amanosan Kongo-ji (Kawachinagano City, Osaka Prefecture) |
| Location | On deposit at the Kyoto National Museum, 527 Chayacho, Higashiyama Ward, Kyoto |
| Public display | Not on permanent view; shown occasionally in Kyoto National Museum exhibitions |
References
- National Database of Designated Cultural Properties (Agency for Cultural Affairs): Ken (Unsigned)
- https://kunishitei.bunka.go.jp/bsys/maindetails/201/400
- Amanosan Kongo-ji Official Website: History
- https://amanosan-kongoji.jp/about/history/
- Kawachinagano City: Amanosan Kongo-ji
- https://www.city.kawachinagano.lg.jp/soshiki/57/62995.html
- WANDER Kokuho: Ken (Unsigned), Kongo-ji
- https://wanderkokuho.com/201-00400/
- Kyoto National Museum
- https://www.kyohaku.go.jp/
Last verified: 2026.06.10