Sataya and Sada Pass Tombs

The Satadani-Satadao Burial Mound Group

Eight earthen tombs sit on a low ridge in the Shōbara Basin, deep in the Chūgoku Mountains of northern Hiroshima Prefecture. Built between the first century BCE and the first century CE, they belong to the Yayoi period, when wet-rice agriculture was reshaping the Japanese archipelago and the first hereditary chieftains were beginning to claim public, monumental graves. The Satadani-Satadao Burial Mound Group preserves an early chapter of that story.

The complex stretches about 250 metres east to west along the crest of a hill some 300 metres above sea level, on the left bank of the Saijō River. The mounds fall into three clusters: Satadani Mounds 1 through 3 on the west, Satadao Mounds 1 and 2 in the middle, and Satadao Mounds 3 through 5 on the east. Together they include three "four-cornered protruding mounds" (yosumi-totsushutsu-gata funkyū-bo), four square platform tombs (hōkei daijō-bo), and one square moated tomb (hōkei shūkō-bo)—a remarkably varied roster for a single hilltop cemetery.

The group was designated a National Historic Site on 11 October 2021. It is only the second site in Shōbara to receive that status, after the Yorikura Rock Shelter, designated in 1969.

The Four-Cornered Protruding Mound and the Birth of Chiefly Graves

Seen from above, a yosumi-totsushutsu-gata funkyū-bo resembles a square with four tongue-like extensions pulled outward from each corner. The form has no parallel anywhere else in the world. It emerged in the upper reaches of the Gō River and its tributaries—the very area where Satadani and Satadao stand—then travelled down the Hino River toward the Japan Sea, where it grew steadily larger and more elaborate. By the late Yayoi period, the rulers of what would become Izumo were being buried under colossal versions of the same form. A few generations later, builders of the early Kofun-period keyhole tombs would inherit several of its distinctive features. In a real sense, the Satadani-Satadao mounds stand near the headwaters of the entire Japanese tradition of monumental tomb building.

Systematic excavation began in 2007, with Hiroshima University's Department of Archaeology and the Shōbara City Board of Education working as joint partners. The fieldwork doubled as a training school for graduate students under Professor Nojima Hisashi, and over six campaigns the team pieced together a precise chronology that earlier surveys, beginning around 1986, had only sketched.

What they recovered was a record of changing ideas about death. The oldest mound at the site, Satadao Mound 3, was built by digging a burial pit, laying the body inside, covering it with earth, then repeating the process with another burial and another layer of fill. The mound grew interment by interment. By contrast, Satadani Mound 1, built only a few generations later at the start of the Late Yayoi, was constructed in the opposite sequence: first the mound was raised to its full height, and only then was a large central pit cut down into its summit.

That reversal—what archaeologists call the shift to "mound-first" construction—was not a mere matter of technique. It reflects the rise of a new kind of social actor. The central burial in Satadani Mound 1 occupies a stage prepared in advance, surrounded by smaller subsidiary pits for retainers or relatives. Stones line the foot of the mound, more stones face its slopes, a small protruding section extends outward from the body of the tomb, a wooden chamber (mokkaku) encloses the coffin, and a large red-painted vessel was set above the pit as part of the funeral. Almost every feature that would later define the monumental tombs of Izumo, northern Kibi, and the Tango Peninsula appears here, in compact and early form.

Why This Site Was Designated

What sets the Satadani-Satadao group apart, in the judgement of the Agency for Cultural Affairs, is the unusual completeness with which one hilltop preserves the transition. Across a span of roughly two centuries, on a single ridge built up by what was almost certainly a single community, the form of the tomb, the method of construction, the placement of burial pits, and the equipment of funeral ritual all change in step.

Pottery tells a parallel story. In the earliest graves, the vessels placed around the mound were produced locally, in styles native to the Bingo highlands. By the Late Yayoi, ceramics from the Kibi region of present-day Okayama appear among them, and pots begin to be set on top of the burial pit rather than beside it. The community at Shōbara was tightening its ties with neighbours to the south and east, while its own leaders were stepping forward as individuals worthy of distinct, prepared graves.

For specialists working on the formation of early Japanese society, this combination—visible change in the same place, across a short span, recorded with stratigraphic clarity—is rare and valuable.

What to Look For on Site

The site is open countryside. National Route 183 and its newer bypass, the Kō Road, cut between the three clusters of mounds, with pedestrian footbridges linking them. Visitors today see Yayoi-period tombs and modern highway engineering occupying the same hilltop, an unusual juxtaposition that Japanese heritage sites rarely offer.

The protruding corners of the four-cornered mounds are the most distinctive feature, but their geometry can be hard to read from a single vantage point because two thousand years of weathering have softened the edges. Satadao Mound 3, carefully exposed at one corner during the 2008 field season, is a particularly important example: it belongs to the early phase of the form, when the protrusions were still modest and the mound itself was small.

The richest single artefact recovered from the group is a spouted, pedestal-footed bowl-shaped vessel from Satadani Mound 3. Standing 55.5 centimetres tall, it was almost certainly made for funeral use rather than daily life. It is not on permanent display, so seeing the original means catching a special exhibition. Photographs of it appear in the Shōbara City and Hiroshima Prefecture archaeological publications listed below.

From the crest of the ridge, the meander of the Saijō River curls below, and ridge after ridge of the Chūgoku Mountains rises away to the north. Stand on the ground itself and the choice of site, made by people two thousand years ago, suddenly makes sense without explanation.

Around the Site and How to Visit

The mounds form an outdoor archaeological park without a dedicated visitor centre or on-site interpretive exhibits. Entry is free and there are no opening hours. Travellers are advised to come by car: a stretch of the route runs alongside a busy national road, and the three clusters of mounds are linked only by pedestrian bridges, so navigating on foot from the nearest station is awkward. The Shōbara Interchange on the Chūgoku Expressway is roughly five minutes' drive away, and Bingo-Shōbara Station on the JR Geibi Line is about ten minutes away.

Bihoku Hillside Park (Kokuei Bihoku Kyūryō Kōen), a vast national park a few kilometres away, makes a natural pairing for a half-day or full-day visit. The landscape there is gentler—seasonal flower beds, walking trails, and the kind of cultivated woodland the Japanese call satoyama—and it offers an immediate sense of the topography that drew Yayoi-period settlers to the basin.

For deeper background on the archaeology of northern Hiroshima, the Taishaku-kyō Museum (Jiyūkan) in the Tōjō district to the east displays material from the Yorikura Rock Shelter and the wider Taishaku Gorge cave sites, the same prehistoric world from which the Satadani-Satadao communities ultimately descended. The museum has hosted special exhibitions devoted to the burial mound group in the past—most notably "The Birth of a Yayoi Royal Tomb in the Shōbara Basin" in 2019–2020—and may do so again, so it is worth checking current schedules before travelling.

Shōbara as a whole rewards travellers who plan more than a day. The municipality contains over two thousand recorded archaeological sites, plus living traditions designated as Important Intangible Folk Cultural Properties such as the Hiba-Kōjin-kagura ritual dance and the Shiobara no Daisen Kuyō Taue rice-planting ceremony. The Satadani-Satadao mounds gain in resonance when seen as part of this longer story of the Chūgoku highlands.