Shijimizuka Site: A Jomon Village Beside Lake Sanaru
The name Shijimizuka means "clam mound," and it describes the ground itself. Local people knew long ago that the low plateau here was full of freshwater clam shells, well before anyone understood why. The answer lies about three thousand years in the past, when a small community of the Jomon period lived on this rise of land in what is now western Hamamatsu, eating shellfish gathered from a nearby lake and leaving the shells in heaps that survive to this day.
The site now sits inside Shijimizuka Park, a quiet green space reachable by a short bus ride from Hamamatsu Station. Walking paths lead past the old shell mounds, reconstructed pit dwellings stand where Jomon houses once stood, and a covered shelter lets visitors look straight into a wall of packed clam shells more than a meter thick. The Hamamatsu City Museum next door holds the pottery, tools, and even human remains recovered from the ground.
A Settlement of the Late Jomon Period
Shijimizuka was a village of the Late and Final Jomon period, occupied roughly between 4,000 and 3,000 years ago. It stands on the Mikatahara plateau, about one kilometer northeast of Lake Sanaru, which in the Jomon period was a brackish inlet open to the sea.
Archaeologists believe people lived here for around a thousand years. The community itself was small. At any single moment perhaps five houses stood on the plateau, arranged around an open central space, with a burial ground close by. Excavations have identified the remains of more than twenty dwellings and around thirty graves accumulated across the whole span of occupation.
The four shell mounds give the site its name. Over ninety percent of the shells are Yamato-shijimi, a small brackish-water clam that thrives where rivers meet the sea. The people here also gathered hard clams, oysters, and other shellfish, and they hunted and fished widely. Bones recovered from the mounds include deer and wild boar, carp and sea bream, and animals as large as whales and sea turtles.
Why the Site Matters
Japan has many Jomon shell mounds, but most lie along the Pacific coast of eastern Japan. In the Tokai region, and Shizuoka Prefecture in particular, they are rare. Shijimizuka is the most substantial example in the area, which made its preservation a matter of national importance.
The plateau soil is acidic, and acidic ground normally destroys bone and shell within a few generations. The shell mounds changed that. The calcium in the heaped clam shells neutralized the soil around them, so organic material that would have vanished elsewhere stayed in the ground. Human skeletons, animal bones, and worked tools of antler and bone all survived because the discarded shells protected them.
That preservation is the source of the site's scientific value. The shell layers can be read like the pages of a book, their order revealing how the village grew and changed. The Agency for Cultural Affairs designated Shijimizuka a National Historic Site on 13 May 1959, and the protected area was expanded in 1984.
What to See on a Visit
The clearest impression of the site comes at the First Shell Mound, where a roofed structure protects an exposed section of the midden. The wall of shells rises about 1.5 meters. Each band of clam shells represents food eaten and discarded by people who lived here, layer settling on layer for a thousand years. Standing in front of it gives a direct sense of how long this small community endured.
Elsewhere in the park, reconstructed pit dwellings with thatched roofs mark the locations of excavated houses. Visitors can step inside and see the sunken floor and central hearth that defined a Jomon home. Signboards at the Second and Third Shell Mounds point out post holes and hearths, though the features themselves have been reburied for protection.
One discovery on display at the museum next door brings the people themselves into focus. According to the museum, the burial ground yielded the skeleton of an older man, thought to have been about seventy, laid in an oval pit with his limbs drawn up and a shell bracelet still on his arm. The pottery is just as telling. Early vessels follow eastern Japanese styles, while later ones show western Japanese techniques, a sign that the village sat along routes of exchange that crossed the whole archipelago.
The Museum and the Park
The Hamamatsu City Museum shares the grounds with the site and works as its natural starting point. Its permanent exhibition traces the history of the Hamamatsu area from prehistory onward, and the rooms on the Jomon period display pottery, shell bracelets, clay earrings, and bone tools excavated from Shijimizuka itself. A model of a Naumann elephant greets visitors at the entrance, a reminder of the even older Ice Age past of this region.
Shijimizuka Park is open ground with free parking, pleasant for a slow walk in any season. The museum charges a modest admission fee, around 310 yen for adults at the time of writing, with free entry for elementary and junior high school students. The interiors of the reconstructed dwellings can be entered during museum opening hours, weather permitting.
Hamamatsu is well known for grilled eel and for its own style of gyoza dumplings, and the city center near the station has plenty of places to try both. Pairing a morning at the site with lunch in town makes for an easy half-day plan.
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Q&A
- How old is the Shijimizuka Site?
- It dates to the Late and Final Jomon period, roughly 4,000 to 3,000 years ago. The community is thought to have lived on the plateau for about a thousand years.
- What is a shell mound, and why is this one important?
- A shell mound is an accumulation of discarded shells, bones, and other refuse left by ancient people. Shell mounds are rare in Shizuoka Prefecture, and Shijimizuka is the largest in the area. The calcium in its shells preserved bone and organic material that the acidic local soil would otherwise have destroyed.
- Can I go inside the reconstructed houses?
- Yes. Reconstructed thatched pit dwellings stand in the park, and their interiors can be entered during museum opening hours when weather permits.
- How do I get there from Hamamatsu Station?
- Take a bus from the Hamamatsu Station bus terminal toward Shijimizuka and Sanarudai. The ride takes about 15 minutes; get off at the museum stop, a minute or two from the park entrance. Free parking is available for those arriving by car.
- Is there an entrance fee?
- The park itself is free to enter. The adjacent Hamamatsu City Museum charges a modest admission fee for adults, with free entry for elementary and junior high school students. Visitors are encouraged to see both together.
Basic Information
| Name | Shijimizuka Site (蜆塚遺跡) |
|---|---|
| Location | Shijimizuka, Hamamatsu City, Shizuoka Prefecture |
| Designation | National Historic Site |
| Date designated | 13 May 1959; protected area expanded 25 July 1984 |
| Period | Late to Final Jomon period (c. 4,000–3,000 years ago) |
| Main features | Four shell mounds, dwelling sites, and a burial ground |
| Adjacent facility | Hamamatsu City Museum |
| Access | About 15 minutes by bus from Hamamatsu Station; alight at the museum stop |
| Opening | Shijimizuka Park is open daily and free; reconstructed dwellings can be entered during museum hours |
References
- Database of National Cultural Properties, Agency for Cultural Affairs — Shijimizuka Site
- https://kunishitei.bunka.go.jp/bsys/maindetails/401/1361
- Hamamatsu City Museum (official site)
- https://www.city.hamamatsu.shizuoka.jp/hamahaku/
- Hamamatsu City — The Shell Mounds of the Shijimizuka Site
- https://www.city.hamamatsu.shizuoka.jp/hamahaku/04smzkap/kaizuka.html
- Hamamatsu City — Museum Collection: Jomon Period / Artifacts from the Shijimizuka Site
- https://www.city.hamamatsu.shizuoka.jp/hamahaku/03kanzo/jyoumon2.html
Last verified: 2026.05.27