Yato Castle Ruins

Yato Castle Ruins: An Earthwork Fortress at the Cradle of the Kai Genji

Yato Castle never had stone walls or a tower keep. What survives on the wooded crown of Chausuyama, an 862-meter rise on the southern skirts of Mt. Yatsugatake, is shaped entirely from soil: rings of low ramparts, shallow ditches, and stepped terraces of level ground where timber halls once stood. The site lies in the Yato district of Oizumi, part of Hokuto City in northern Yamanashi Prefecture, and it was designated a National Historic Site on November 29, 1993.

This is a yamajiro, a mountain castle, and one raised long before firearms reached Japan. Visitors expecting battlements will instead find a quiet hilltop where the logic of medieval defense is written in the contours of the ground. Read the slopes carefully and a layout emerges: a central enclosure on the summit, a larger bailey to the east, paired tiers to the north, and a smaller compartment on the west.

The castle carries other names. Locally it is called Chausuyama after the hill itself, and old records also refer to it as Hemi Castle, after the clan whose story begins here.

A Castle Tied to the Birth of the Kai Genji

Local tradition credits the founding of Yato Castle to Hemi Kiyomitsu (逸見清光), a late-Heian warrior remembered as the ancestor of the Kai Genji, the Minamoto lineage that took root in this province. The genealogy reaches back two generations: Kiyomitsu was the son of Minamoto no Yoshikiyo, the first of the family to style himself Takeda, and the grandson of Minamoto no Yoshimitsu, the warrior known as Shinra Saburo.

The family's arrival in Kai was not voluntary. In 1130, after a complaint lodged with the governor of Hitachi Province, Yoshikiyo and Kiyomitsu were exiled to estates scattered across Kai. Kiyomitsu settled in the Hemi estate on the southern flank of Yatsugatake, took the area's name as his own, and built up a base of power there. The volcanic foothills had long supplied horses to the imperial court, and that pastoral wealth helped turn a banished family into a regional force.

Whether the warrior himself stood on this exact summit is something the sources only hint at. Edo-period gazetteers such as the Kai Meishoshi and the Kai Kokushi record a tradition that Kiyomitsu lived and died at a castle in this village. More suggestive still is the Azuma Kagami, the chronicle of the Kamakura shogunate, which notes that in 1180 Hojo Yoshitoki came to a place called Hemiyama to urge the Kai Genji to join Minamoto no Yoritomo's rebellion. At least one later gazetteer identifies Chausuyama with that Hemiyama, which would place a turning point of the Genpei War on this very hill.

The name resurfaces across the centuries. A document of 1351, kept at the Daigoji temple, mentions a "Hemi Castle in Kai" during the upheavals of the Kanno era. Two centuries on, in the age of Takeda Shingen, a campaign diary records a "Yato encampment" near the Bomichi, the straight military road Shingen drove toward the Shinano front. The hill stayed useful because it commanded the route.

Why the Site Was Designated

Yato Castle was protected under the designation criterion covering castle sites and other places connected to political history. Its value rests on two things at once: the wealth of tradition linking it to the early Kai Genji, and the clarity with which its earthworks still record how a regional power organized its defenses.

The Agency for Cultural Affairs frames it as a counterpart to the better-known Takeda strongholds. Sites such as the Takeda Clan Residence, Yogaiyama, and Shinpu Castle preserve the family at the height of its power in the sixteenth century. Yato Castle reaches further back, to the moment the lineage was still putting down roots. Together these places let researchers trace how authority in this corner of Japan grew, generation by generation.

The castle also had a long working life. It was not abandoned after the Heian period but kept its role as a local stronghold through the medieval centuries. Its final chapter came in 1582. After the Takeda were destroyed, the Later Hojo and the Tokugawa fought over the leaderless province in the conflict known as the Tensho-Jingo struggle, and Yato Castle was taken and substantially rebuilt by Hojo forces. The earthworks a visitor walks today owe part of their final form to that last campaign.

What to Look For on the Hill

The pleasure of Yato Castle lies in reading the ground. Start at the summit, where the main enclosure measures roughly 30 meters east to west and 40 meters north to south, ringed by an earthen rampart that rises between half a meter and two meters. Walk its edge and the defensive intent becomes plain.

To the east lies a larger bailey, about 30 by 60 meters, wrapped by a rampart a full two meters high. North of the summit, two stepped enclosures sit behind a double line of earthworks, together spanning some 40 by 50 meters. A smaller compartment occupies the western slope. The castle is restored as a historic park, so the ramparts and ditches have been shaped back toward their original profiles, and explanatory boards help visitors match the mounds to the plan.

Excavations in 1982 and 1989 added detail to the picture. Archaeologists confirmed a trench running along the base of the ramparts and uncovered foundation stones from buildings that once stood within the walls. Among the finds were fragments of a celadon bowl decorated with lotus petals, fifteenth-century earthenware, and Hongwu Tongbao, bronze coins minted in Ming China. These objects place real activity on the hill across several medieval centuries.

There is also a reward for simply standing still. The hill is planted with around 400 cherry trees, Somei-yoshino and double-flowered varieties that open in succession through April. A perimeter path circles the outer park, and gaps in the trees frame Mt. Yatsugatake, Mt. Kaikomagatake, and, on clear days, Mt. Fuji. A small Hachiman shrine stands on the summit, where one record notes Kiyomitsu was enshrined alongside the deity.

The Surrounding Landscape

The castle is the historical anchor of a wider archaeological landscape on the southern Yatsugatake plateau. Just below the hill, the Joka site has yielded the remains of a Heian-period village, including a stone belt fitting of the kind worn as a court rank insignia, along with imported Chinese celadon and white porcelain. This was most likely the central settlement of the Hemi estate, the community from which Kiyomitsu's power grew.

A short distance away lies the Kinsei site, another National Historic Site, this one a ceremonial place of the late Jomon period. Its finds, including a striking hollow clay figure, are displayed at the same museum that interprets Yato Castle, making it easy to pair the two visits.

The Yato name still echoes in nearby toponyms such as Gosho and Machiya, words that hint at residences and a townscape long gone. Kiyomitsu's memorial temple, Seikoji, stands in the Osata area of present-day Nagasaka; its forerunner once stood northwest of the castle. The broader district around the southern foot of Yatsugatake rewards a longer stay, with highland scenery, local sake breweries, and the clear night skies for which the area is known.