Ōtorii-yama Site: A Fortified Residence of the Kiyohara Clan
Two low, river-bounded hills on the eastern edge of the Yokote Basin carry the remains of one of northern Japan's most significant eleventh-century strongholds. The Ōtorii-yama Site sits in the city of Yokote in Akita Prefecture, about two kilometres northeast of the present city hall. The two rises that hold the ruins, Ōtorii-yama and Koyoshiyama, are ringed on three sides by water: the Yokote River to the west, the Yoshizawa River to the north, and the Myōei River to the south.
What the hills preserve is not a temple or a tomb but a residence built for defence. Archaeologists who have worked the ground since 1977 have traced a double line of earthen ramparts and dry moats encircling the living quarters, a layout that places the site among the clearest surviving examples of the kyokan, the fortified manor of the late Heian period. The Agency for Cultural Affairs designated it a National Historic Site in 2010, and in 2017 the nearby Jindate Site was added to the designation under the formal name Ōtorii-yama Site with the Jindate Site appended.
The Kiyohara clan and the wars of the north
In the eleventh century the Yokote Basin formed the core territory of the Kiyohara, a warrior family whose three districts of Yamamoto, Hiraka, and Ogachi covered much of what is now southern Akita. The Kiyohara rose to regional dominance during the Zenkunen War of 1051 to 1062, when they sided with the court commander Minamoto no Yoriyoshi against the Abe clan of Mutsu. A generation later they tore themselves apart in the Gosannen War of 1083 to 1087, the conflict that drew in Minamoto no Yoshiie and ended with the Ōshū Fujiwara inheriting their lands and their power.
Ōtorii-yama belongs to that world. A military chronicle of the Zenkunen War, the Mutsu Waki, records that the Abe warrior Masatō first took shelter with Yoritō, styled Ōtoriyama Tarō, son of Mitsuyori of Dewa. Local tradition has long read the Ōtoriyama of that line as this very hill, and identifies the site as the seat of Kiyohara no Mitsuyori and his son Yoritō. Among the fortified residences named in the war records, Ōtorii-yama is one of the few that can be matched to the ground with real confidence, alongside the Abe clan's Chōkai-no-ki in present-day Iwate.
What the excavations revealed
The site came to light by accident. When the former city of Yokote planned an athletic park on the hills in the 1970s, survey work ahead of construction uncovered the buried defences. Eleven seasons of excavation followed, seven of them at Koyoshiyama from 1977 onward and a further three-year campaign at Ōtorii-yama beginning in 2007.
The defences proved formidable. Around the core of the residence ran two concentric earthen ramparts and two dry moats. The outer rampart reaches 9.2 metres across at its widest and stands 1.6 metres high; the outer moat measures up to 8.8 metres wide and 2.5 metres deep. A palisade lined the inner edge, and buildings interpreted as watchtowers stood along it. Where the outer moat had to be crossed, the builders left an earthen causeway in place.
Inside, the flat ground was split north and south by a broad ditch up to four metres wide. Excavators recorded sixty post-supported buildings at Koyoshiyama alone, seventeen in the northern sector and forty-three in the southern. Most were modest, a single bay square, though larger halls appear from the early eleventh century onward. The buildings fall into three phases: the earliest, in the late tenth century, set on an axis tilted about thirty degrees; the later two, through the eleventh century, aligned closer to true north. On the summit of Ōtorii-yama itself stood the grandest structure found at the site, a hall two bays by five with a pent roof, or hisashi, running around all four sides, approached across a double ditch and an earthen bridge.
The finds add texture to the picture. Wheel-thrown hajiki earthenware dominates, datable to between the late tenth and late eleventh centuries and so contemporary with the two great wars. Among it were sue stoneware, Chinese white porcelain, four-lugged storage jars from the Tokoname kilns, wooden objects including fans, and iron knives. The most telling group is a set of nearly three hundred kawarake, the plain unglazed bowls and dishes used for ritual meals and banquets. Concentrations of kawarake on this scale are rare anywhere in Japan for the period, and they point to formal gatherings held within the ramparts. A near-complete Chinese stone inkstone turned up as well, closely matching one excavated at the Fujiwara administrative site of Yanaginogosho in Hiraizumi.
That resemblance is the heart of the site's importance. The design of Ōtorii-yama, an isolated hill hemmed by rivers and a highway and wrapped in ramparts and moats, anticipates the great twelfth-century residences of the Ōshū Fujiwara, including Yanaginogosho and the Jingamine castle site in Fukushima. Many scholars now think the Fujiwara carried forward building methods first worked out by the Kiyohara. For a region whose early history was long written from documents alone, Ōtorii-yama offers something rarer: a place where the warrior families named in the chronicles can be studied in the earth itself.
Visiting the hills today
The site is open ground, free to enter, and shares its hills with the athletic park whose construction first exposed it. Pool, plaza, and tennis courts occupy much of the level land, so the visible archaeology is concentrated on the southern hill of Ōtorii-yama and the western slope of Koyoshiyama.
The double moat is the feature to look for. Two centuries of silt have softened the cuts, and a visitor expecting a dramatic gorge may be surprised by how shallow they now seem; reading them takes a moment of imagination. The earthen ramparts survive best at Ōtorii-yama, where the ground was never built over. A small shrine, Ōtoriiyama Jinja, crowns the summit on the spot where the great four-sided hall once stood. On the ridge between the park car park and the shrine lies a cluster of small mounds known as the Ōtorii-yama Jūsanzuka, the thirteen mounds, thought to date from the later Kamakura period; the twin moat runs just below them.
Interpretive signs stand at the main points, though they are chiefly in Japanese. Visitors who want the fuller story do well to pair a walk here with a stop at one of Yokote's museums, where excavated kawarake and the inkstone are explained in context.
The wider landscape of the Gosannen War
Ōtorii-yama is one stop on a trail of battlefields. The Gosannen War unfolded across this part of the basin, and its other named strongholds lie within easy reach. The presumed site of Kanezawa-no-ki, the fortress where the fighting reached its bitter climax, is now Kanezawa Park, a short drive north; the site of Numa-no-ki lies to the southwest. The Jindate Site added to the Ōtorii-yama designation in 2017 is itself a candidate location for Kanezawa-no-ki, and it yielded a four-sided eaved hall strikingly like the one on Ōtorii-yama's summit.
Yokote rewards a longer visit. The city is known for its February kamakura festival, when hundreds of snow huts glow with candlelight, and for Yokote yakisoba, a fried-noodle dish served with a fried egg and pickled ginger. The Masuda Manga Museum, the first public museum in Japan devoted to original manga artwork, sits a little further out, as does the Akita Furusato Mura cultural complex.
Yokote Station, on the JR Ōu Main Line, is the gateway; the site lies a short taxi ride to the northeast. Drivers will find the athletic park signposted and parking free.
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Q&A
- What exactly is the Ōtorii-yama Site?
- It is the buried remains of a fortified residence rather than a castle of the later samurai type. Two hills carry double earthen ramparts and dry moats enclosing post-supported buildings, occupied mainly between the late tenth and late eleventh centuries.
- Who lived here?
- The site is identified with the Kiyohara, the warrior clan that dominated the Yokote Basin. The Mutsu Waki names Kiyohara no Mitsuyori and his son Yoritō, and local tradition places their seat on these hills.
- Is there much to see, or only signboards?
- The earthworks survive best at Ōtorii-yama, where you can walk the ramparts and trace the double moat. They are weathered and low rather than dramatic, so it helps to read the interpretive signs first. The summit shrine and the thirteen mounds add interest to the walk.
- How long does a visit take, and is there an entry fee?
- The site is free and always open. A focused walk of the visible remains takes about an hour; combining it with the nearby Gosannen War sites makes a half-day outing.
- When is the best time to visit?
- Late spring through autumn gives the clearest views of the earthworks. Winter in Yokote brings heavy snow that buries the ground features, though it is also the season of the city's celebrated kamakura festival.
Basic Information
| Name | Ōtorii-yama Site with the Jindate Site appended (Ōtorii-yama Iseki) |
|---|---|
| Location | Ōtori-machi and Shinzaka-machi, Yokote City, Akita Prefecture |
| Designation | National Historic Site (designation criterion 2: sites relating to politics) |
| Designated | 22 February 2010; Jindate Site appended 13 October 2017 |
| Designated area | Approximately 120,479 square metres |
| Period | Ancient to medieval; fortified residence occupied mainly from the late 10th to the late 11th century |
| Associated with | The Kiyohara clan; the Zenkunen War and the Gosannen War |
| Access | About 2 km northeast of Yokote City Hall; a short taxi ride from Yokote Station on the JR Ōu Main Line. Free parking at the adjoining athletic park. |
| Admission | Free; the site is open ground with no fixed hours |
References
- Database of National Cultural Properties, Agency for Cultural Affairs — Ōtorii-yama Site with the Jindate Site appended
- https://kunishitei.bunka.go.jp/bsys/maindetails/401/00003656
- Yokote City Official Website — Ōtorii-yama Site (Gosannen War pages)
- https://www.city.yokote.lg.jp/gosannen/1001607/1003577.html
- Comprehensive Database of Archaeological Site Reports Japan, Nara National Research Institute for Cultural Properties — Ōtorii-yama Site
- https://sitereports.nabunken.go.jp/49299
Last verified: 2026.05.22