Aku Site: A 7,000-Year-Old Jomon Ceremonial Center in the Yatsugatake Highlands
High on a forested ridge at the southwestern foot of Mt. Yatsugatake, in Hara Village, Nagano Prefecture, lies one of the most remarkable archaeological discoveries of postwar Japan. The Aku Site (阿久遺跡, Akyū Iseki) is an Early Jomon-period settlement and ceremonial complex dating back roughly 7,000 to 6,000 years. It contains what is currently considered the oldest known annular stone arrangement in Japan — a vast, ring-shaped ceremonial monument that reshaped scholars' understanding of Jomon society.
Designated a National Historic Site in 1979, the Aku Site offers visitors a rare glimpse into the spiritual life of prehistoric Japan, set against the breathtaking backdrop of the Yatsugatake mountains and the sacred peak of Mt. Tateshina.
An Accidental Discovery That Changed Japanese Archaeology
The Aku Site was uncovered in 1975 during preparations for the construction of the Chuo Expressway, the major highway linking Tokyo with central Japan. What was initially thought to be a routine survey quickly revealed evidence of a Jomon village of unprecedented scale and complexity.
Four seasons of excavation between 1975 and 1978 exposed an extraordinary archaeological landscape: dozens of Early Jomon pithouse foundations, more than 800 pits, square arrangements of large posts, and — most stunning of all — a massive ring of stones forming what appears to be a sacred precinct centered on a standing stone aligned with Mt. Tateshina.
The discovery sparked a national debate. Should the ridge be flattened to allow the highway to proceed as planned, or should the site be preserved? After intense discussions, the route of the Chuo Expressway was redesigned, and the site was carefully reburied beneath the roadway in a unique act of underground preservation. Today, much of the Aku Site rests safely beneath the highway, while a portion of the surface has been opened for public viewing with interpretive signage.
Why the Aku Site Was Designated a National Historic Site
On July 2, 1979, the Aku Site was designated a National Historic Site (国史跡) by the Japanese government, recognized for its exceptional archaeological and cultural value. Several features made the designation almost inevitable.
The Oldest Known Annular Stone Arrangement in Japan
The site's centerpiece is a colossal ring of stones (環状集石群, kanjō shūsekigun) — approximately 120 meters along its long axis, 90 meters across its short axis, and 30 meters wide. The ring is composed of around 271 distinct stone clusters, built using an estimated 100,000 to 300,000 cobble-sized river stones. No earlier example of such a large-scale annular arrangement has been confirmed anywhere in the Japanese archipelago.
A Ceremonial Center That Faces Mt. Tateshina
At the heart of the ring stands a single upright stone — a column of granodiorite roughly 120 centimeters tall and 35 centimeters wide. Extending from it in a straight line are eight large flat andesite slabs. The alignment was deliberately oriented so that a person standing at the central stone would gaze directly toward the sacred peak of Mt. Tateshina. Burnt residues on some of the stones suggest fire-based rituals were performed here.
A Window into the Birth of Jomon Ceremonial Life
The Aku Site preserves a clear sequence of cultural change across the Sekiyama, Kuroshima, and Moroiso A and B sub-periods of Early Jomon. Archaeologists can read, layer by layer, how a horseshoe-shaped residential village gradually transformed into a sacred precinct as houses dwindled and ceremonial structures expanded. This rare visibility into the transition from "village of the living" to "place of ritual and the dead" makes the site a keystone for understanding the spiritual evolution of Jomon society.
Highlights and Things to Appreciate
The Standing Stone and Stone Alignment
The standing stone at the center of the ceremonial precinct is the symbolic heart of the Aku Site. Imagining ancient people gathering here to face Mt. Tateshina across the highland landscape — perhaps watching the sunrise, lighting fires, and offering ceremonies — is one of the most evocative experiences a visitor to Japan can have.
The Square Post-Pillar Arrangements
One of the most enigmatic features of the site is a series of square arrangements of large post holes, each side measuring around five to seven meters, with deep pits suggesting massive timber pillars. Their function remains debated: storage buildings, raised-floor structures, or ceremonial enclosures. Square post arrangements of this type are extremely rare in Early Jomon Japan, and most known examples come from this very region of Nagano.
The Burial Landscape
Roughly 700 small pits within and around the stone ring are believed to be graves, possibly used for secondary burials in which bones were re-interred after the body had decomposed. The integration of burial space, ceremonial center, and residential village within a single settlement reveals how thoroughly intertwined daily life and the sacred were for Jomon people.
The Pottery and Stone Tools
Excavations recovered a remarkable range of Jomon pottery — including unusual pedestaled ceremonial bowls found near the standing stone — alongside polished stone axes, grinding stones, and obsidian tools. Many of these artifacts can be viewed today at the Yatsugatake Museum of Art and the Nagano Prefectural Museum of History.
Visiting the Aku Site
Because most of the Aku Site is preserved underground beneath the Chuo Expressway, visitors do not see exposed ruins in the way they might at other archaeological parks. Instead, the experience is one of contemplation: walking across the ridge with explanatory panels nearby, gazing toward Mt. Tateshina along the sightline the ancient builders chose, and imagining the ceremonial life of 7,000 years ago.
The artifacts and the story of the site are presented in detail at the nearby Yatsugatake Museum of Art (Hara Village Folk Museum), only a short drive away. The museum itself, designed by the celebrated architect Togo Murano in 1979, is an architectural treasure in its own right, with continuous dome-shaped roofs nestled into a larch forest at 1,350 meters elevation.
Surrounding Attractions
The Aku Site sits within one of Japan's richest concentrations of Jomon-period archaeology, often called the "Yatsugatake Southwestern Foothills Site Group." Travelers interested in prehistoric Japan can easily make a multi-site Jomon pilgrimage:
- Togariishi Stone Age Site (Chino City) — a National Special Historic Site representing the height of Middle Jomon culture, with reconstructed dwellings and an excellent museum.
- Idojiri Archaeological Site Group (Fujimi Town) — celebrated for its dramatic Jomon pottery, including pieces designated as National Important Cultural Properties.
- Yatsugatake Museum of Art / Hara Village Folk Museum — the local hub for Aku Site artifacts and interpretation.
- Mt. Tateshina — the sacred peak that aligns with the Aku Site's standing stone, offering hiking trails and panoramic highland views.
- Tateshina Highlands and Suwa region — known for hot springs, lakes, and scenic drives, ideal for combining cultural and natural sightseeing.
- 📍 Plan Your Visit to Nagano
- Find tours, activities & transport passes near Aku Ruins
- [ Matsumoto Castle & Kamikochi Hiking Tours ]
Q&A
- How old is the Aku Site?
- The site dates from the Early Jomon period, roughly 7,000 to 6,000 years ago. The annular stone arrangement at its center is currently considered the oldest of its kind in Japan.
- Can I see the actual ruins on site?
- Most of the site is preserved underground beneath the Chuo Expressway. Visitors can walk the ridge and read interpretive signs, but the main archaeological features themselves are not exposed. Excavated artifacts and detailed displays are presented at the Yatsugatake Museum of Art nearby.
- Why is the standing stone aligned with Mt. Tateshina?
- Researchers believe the alignment reflects a ritual relationship between the Jomon community and the sacred peak. Mt. Tateshina dominates the eastern horizon, and the central stone and its line of slabs guide the eye directly toward the mountain, suggesting acts of veneration toward natural landmarks.
- How do I get to the Aku Site and the Yatsugatake Museum?
- The Yatsugatake Museum of Art is about 25 minutes by car from JR Chino Station, 15 minutes from JR Fujimi Station, or 10 minutes from the Suwa-Minami Interchange of the Chuo Expressway. The Aku Site itself is a short drive from the museum.
- Why was the highway built on top of the site?
- The Aku Site was discovered during construction work for the Chuo Expressway. After intense discussion, the highway was redesigned and the site was carefully reburied beneath the roadway, a method chosen to protect the archaeological layers from further disturbance. It is one of Japan's most distinctive examples of underground preservation of a major site.
Basic Information
| Name | Aku Site (阿久遺跡 / Akyū Iseki) |
|---|---|
| Designation | National Historic Site (designated July 2, 1979) |
| Period | Early Jomon period (approximately 7,000–6,000 years ago); also includes traces from Middle Jomon, Late Jomon, and Heian periods |
| Location | Kashiwagi, Hara Village, Suwa District, Nagano Prefecture |
| Elevation | Approximately 900 meters above sea level |
| Setting | Ridge between the Aku River and Ohaya River, at the southwestern foot of Mt. Yatsugatake |
| Excavation | 1975–1978, in conjunction with construction of the Chuo Expressway |
| Key Features | Annular stone arrangement (approx. 120 × 90 m), central standing stone and stone alignment oriented toward Mt. Tateshina, square post-pillar arrangements, approximately 700 burial pits, dozens of pithouses |
| Related Museum | Yatsugatake Museum of Art (Hara Village Folk Museum), 17217-1611 Hara, Suwa District, Nagano 391-0115; tel. +81-266-74-2701; open 9:00–17:00 (last entry 16:30) |
| Access | Approx. 25 min by car from JR Chino Station; 15 min from JR Fujimi Station; 10 min from Suwa-Minami IC, Chuo Expressway |
References
- Cultural Heritage Online — Aku Site
- https://bunka.nii.ac.jp/heritages/detail/190782
- Aku Site — Wikipedia (Japanese)
- https://ja.wikipedia.org/wiki/阿久遺跡
- Hara Village Official Site — Cultural Heritage Guidebook
- https://www.vill.hara.lg.jp/docs/159.html
- Yatsugatake Museum of Art (Hara Village Folk Museum)
- https://yatsubi.com/
- Jomon Japan Heritage — Aku Site
- https://jomon.co/point/detail/95/
- Suwa-Tabi — Exploring the Secrets of the Aku Site
- https://suwa-tabi.jp/news/11912/
- Kotobank — Aku Site (Encyclopedic Entry)
- https://kotobank.jp/word/阿久遺跡-166444
Last verified: 2026.05.04