Remains of Kaminokuni Castle / Remains of Hanazawa Castle /

Three Forts Above the Sea of Japan

On a grassy ridge in the town of Kaminokuni, on the western coast of Hokkaido's Oshima Peninsula, three medieval fortified residences sit within a short distance of one another. Known together as Kaminokuni Tate-ato, they are the remains of Hanazawa-date, Suzaki-date, and Katsuyama-date, built by settlers from the Japanese mainland during the fifteenth century. The Japanese word tate (or date) refers to an earthwork stronghold rather than a stone castle, and these three preserve the layered banks, dry moats, and hillside terraces of a frontier that few visitors associate with Hokkaido.

The settlers here were Wajin, ethnic Japanese who had crossed the Tsugaru Strait and were called watari-tō, "the people who came over." They lived alongside, traded with, and at times fought the Ainu, the Indigenous people of the northern islands. The three forts mark the moment when that contact hardened into the political order that would eventually become the Matsumae domain.

A Frontier of Three Districts

In the mid-fifteenth century the southern tip of Hokkaido lay under the authority of the Andō clan of Tsugaru, who divided the coast into three administrative areas, each with its own warden: Shimonokuni in the east, Matsumae in the centre, and Kaminokuni in the west, around the mouth of the Amanogawa River. Kaminokuni held one of the region's principal harbours, a foothold for the maritime trade that ran up the Sea of Japan.

Wajin settlement bred friction. In 1457 a long-simmering grievance broke open into Koshamain's War, an uprising of Ainu led by a chief remembered as Koshamain. Several Wajin forts fell. Hanazawa-date, held by the warden Kakizaki Suesige, did not. The records credit a young retainer, Takeda Nobuhiro, with killing Koshamain and breaking the revolt. Nobuhiro married a daughter who had been adopted into Kakizaki Suesige's household and took on the leadership of the Kakizaki line, the clan that would rename itself Matsumae a century and a half later.

Reading the Three Sites

The forts can be read in sequence, oldest to newest, and each is larger than the one before. Hanazawa-date is the earliest, a hill fort running about 200 metres north to south, up to 80 metres wide, and rising roughly 50 metres from its foot to the summit in six broad terraces. Excavation behind the fort found a defensive ditch 11 metres across and 3.9 metres deep, along with fifteenth-century Chinese celadon and white porcelain, a Suzu-ware grinding bowl, iron nails and saws, and a cache of some 2,000 coins recovered near the summit. The pottery is entirely fifteenth century, which tells archaeologists the fort was already abandoned before its neighbour rose to prominence. The written record agrees: the Matsumae chronicle Fukuyama Hifu places the death of Kakizaki Suesige in 1462.

Suzaki-date is the one fort in all of Hokkaido whose founding date is firmly documented. According to Shinra no Kiroku, the oldest record produced in Hokkaido, Takeda Nobuhiro built it in 1457, the same year he turned the tide of Koshamain's War, and marked the occasion with a ceremony the chronicles describe in grand terms. Digging here has turned up celadon, white porcelain, and Suzu ware of the fourteenth and fifteenth centuries, around 2,500 coins, and post holes from timber buildings. The finds cluster not on the sandy high ground but along the old course of the Mena River, near the approach to Sunadate Shrine. Older layers complicate the story: Satsumon pottery from around the tenth century, Sue ware from Goshogawara in Aomori, and Haji earthenware show that people were living and trading at this river mouth fully five centuries before Nobuhiro arrived.

Katsuyama-date is the largest and the most thoroughly studied, spreading across roughly 350,000 square metres on the slope of Mt. Iō. Nobuhiro built it once his grip on the western coast was secure; the fort's guardian shrine was founded in 1473, which fixes the construction close to that year. For some 130 years, until the end of the sixteenth century, it served as the political, military, and trading heart of the Takeda and Kakizaki families on the Sea of Japan side of the island.

Why the Site Matters

More than two decades of excavation at Katsuyama-date have produced well over 100,000 objects, including around 50,000 pieces of ceramic. The range is telling: Chinese celadon, white porcelain, and blue-and-white sit beside domestic Mino and Echizen wares, the spread of a community plugged into long-distance trade. Archaeologists have also traced buildings, wells, dry moats, and bridges, and below the fort the outline of a town. Taken together, the evidence supports calling the place a medieval city, an unexpected claim for fifteenth-century Hokkaido.

One category of find carries particular weight. More than 500 bone and antler tools of Ainu make have come out of the ground inside the fort. The historian Amino Yoshihiko read this as near-proof that Ainu and people from the mainland were living together within the same walls. The site has become a standard reference for what Japanese textbooks call "the medieval north," and its layers of daily life keep that argument grounded in physical things rather than legend.

Visiting Today

Katsuyama-date is the fort set up for visitors. Wooden palisades, dry moats, and bridges have been reconstructed in three dimensions, while the footprints of buildings and wells are marked at ground level, and explanatory boards along the paths let you follow the layout as you walk. The site is registered among Japan's Continued Top 100 Castles.

Start at the Katsuyama Castle Guidance Facility at the foot of the slope. A 1:200 model of the fort sits where you can compare it through the window with the real terrain outside, and a video traces the history of the northern Middle Ages with a computer reconstruction built from the excavation data. Beneath the building, seven graves from the Iōzan burial ground have been cast and replaced exactly where they were found, a quiet reminder that the people of the fort are buried on the same hill. Takeda Nobuhiro himself died in 1494 and was laid to rest at the summit of Mt. Iō, which today gives a wide view over the Sea of Japan.

Walking the ridge between the three forts, you can also reach several other monuments of old Kaminokuni: the Main Hall of Jōkokuji and the Old Sasanami Residence, both Important Cultural Properties, and the main hall of Kaminokuni Hachimangū, designated by Hokkaido. An annual memorial for Koshamain is held near Katsuyama-date in early July.