Excavated Items from Koda Shell Mound, Chiba Prefecture

Kōde Shell Mound Artifacts: Early Jōmon Life in 266 Objects

Among the pottery dug from the Kōde shell mound in Matsudo, one habit keeps catching the eye. A great many of the medium-sized cooking pots carry a small pouring spout, the way a modern jug might. Spouted vessels turn up often enough here that archaeologists treat them as a local fingerprint, something that marks a pot as belonging to this particular village rather than another along the river.

Those pots are part of a set of 266 objects excavated from a settlement that stood on this plateau roughly 6,000 years ago. In June 1994 the whole group was registered together as a national Important Cultural Property, classed as archaeological material. The collection is kept at the Matsudo City Museum, about an hour by train from central Tokyo.

The people who made and used these things belonged to the Jōmon culture, the hunting, fishing and gathering communities of the Japanese archipelago. The word Jōmon means "cord-marked," after the impressions rolled into the surface of their clay vessels. Jōmon potters were working in fired clay thousands of years before agriculture reached these islands, which places their craft among the oldest pottery traditions anywhere in the world. The Kōde finds come from the first half of the Early Jōmon, a window when the makers were already capable of work that is both technically assured and quietly inventive.

A village beside a vanished shoreline

Kōde sits at the western edge of the Shimōsa Plateau, on a tongue of high ground about eighteen metres above sea level. A small river curls below it before joining the Edo River, and the plateau falls away on three sides. It is, in other words, exactly the kind of place a Jōmon community liked: dry ground with a view, fresh water close by, and easy reach to richer hunting and foraging.

The shells that give the site its name explain something surprising about its setting. Today Matsudo lies well inland. Six thousand years ago, at the peak of the postglacial sea-level rise that Japanese archaeologists call the Jōmon transgression, a saltwater inlet pushed almost to the foot of this slope. The mound is built largely from marine shells, hard clams and ark shells among them, the leftovers of countless meals gathered from a coast that has since drawn kilometres away. Read the shells and you are reading a drowned coastline.

A "shell mound" is essentially a refuse heap, but an unusually generous one for anyone trying to reconstruct daily life. The calcium in the discarded shells keeps the surrounding soil alkaline, which slows the decay of bone, antler and other organic matter that would normally rot away. Alongside the shells, the Kōde excavations turned up animal and fish bones and even charred walnuts, the kind of evidence that lets researchers put real food on a prehistoric table.

The settlement itself was large. Its remains spread roughly 250 metres north to south and 180 metres east to west, with about fourteen separate clusters of shell debris arranged in a rough horseshoe around the plateau edge. More than 150 pit-dwelling floors have been traced across the site, and later excavations pushed the count past 160. The 266 designated objects were recovered from these dwellings and the surrounding cultural layers during a long campaign of digs run by the Matsudo City Board of Education from 1971 onward, more than fifteen seasons in all stretching into the late 1990s. Trial excavations decades earlier, in the 1940s and 1950s, had already drawn the attention of some of the scholars who helped build the chronology of the Jōmon period.

Why the collection was singled out

What earns a box of broken pottery and stone tools a national designation is rarely a single spectacular piece. Here it is completeness. The Kōde group preserves nearly the full range of things a community needed to live, and it does so for a slice of the Early Jōmon that is otherwise thinly represented.

Pottery makes up the heart of it: 95 deep bowls, six shallower bowls and five small vessels, a quantity and quality that few comparable sites can match for this phase. Almost all of it belongs to two well-known styles, the Hanazumi Lower type and the Sekiyama type, both dating to the first half of the Early Jōmon. Because the Kōde material is so abundant and so cleanly dated, scholars use it as a reference standard, a yardstick against which finds from other sites can be measured.

Around the pots sits the rest of the toolkit. The stone tools alone include polished and chipped axes, 27 rough pebble tools, eight stone knives, six drills, 61 arrowheads, and a striking number of grinding stones and pitted stones used to process plant food. That emphasis on milling equipment is telling: these were not people who lived on shellfish alone, and the charred walnuts from the mound back this up. The collection also holds personal ornaments, slit stone earrings and beads, shell knives and a fragment of shell bracelet, a pendant carved from a wild boar's tusk, and a pair of bone or antler points for piercing. Taken together, the objects sketch a rounded picture of a working settlement rather than a single activity.

One quieter detail rewards attention. Mixed in among the locally made wares are a few pots of the Kojima type, a style whose home territory lies in the Tōkai and Chūbu regions of central Japan. Their presence at a site near present-day Tokyo is evidence that goods, ideas, or people were moving over considerable distances this early, a reminder that the Jōmon world was connected rather than sealed off valley by valley.

What to look for

If you can see the pottery in person, slow down at the deep bowls. The larger ones flare dramatically at the rim, their mouths rising and dipping in a wave while the neck pinches in below. The medium bowls are plainer in profile, opening in a straight line from a flat base, and it is these that so often carry the little spout. Look closely at the body and you may notice fine channels and pockmarks in the clay. Those are the ghosts of plant fibres, deliberately mixed into the paste before firing, then burned away in the kiln. Fibre-tempered clay like this is a hallmark of Early Jōmon potting.

Then there is the decoration that gives the whole period its name. Jōmon potters pressed and rolled twisted cords across the wet surface of a vessel to leave repeating patterns. At Kōde the range is wide: simple diagonal cord marks, a feather-like herringbone made by rolling cords wound in opposite directions, grounds of braided-cord impression overlaid with parallel incised lines, neat arcs drawn as if with a compass, and small applied knobs standing proud of the surface. Seen up close, what can look from a distance like rough texture resolves into careful, almost musical repetition.

The smaller finds carry their own appeal. The slit stone earrings, known in Japanese as ketsu, are rings cut with a single gap so they could be slipped onto the ear, a form of body ornament that Jōmon people shared with contemporaries across East Asia. The boar-tusk pendant is a more personal object still, a curve of ivory worked into something to be worn and seen. Standing in front of a case of these things, the distance of six thousand years narrows to the width of a glass panel.

The Matsudo City Museum that holds the collection sits inside a large public park and tells the story of the area from the Stone Age to the postwar housing estates, complete with a reconstructed pit dwelling on its grounds and a full-scale 1960s apartment that has become its best-loved exhibit. The museum is a working collection, so which specific designated pieces are on view varies, and special exhibitions devoted to Kōde have appeared from time to time. One important practical note for 2026: the building is temporarily closed for facility work and is scheduled to reopen on 1 September 2026. Anyone planning a visit should check the museum's website for the current display and opening status before setting out.

Around the museum

The museum stands within the Forest and Park of the 21st Century, a green expanse of about 50 hectares with ponds, open lawns and walking paths that make an easy half-day on their own. The outdoor reconstructed dwelling here is the closest you can get to standing inside the kind of house the Kōde villagers built.

Matsudo rewards a wider wander. Near Matsudo Station, Tojo-tei is a refined late-nineteenth-century residence built by Tokugawa Akitake, younger brother of the last shogun, and is itself an Important Cultural Property; its garden and the view from the hill are worth the short climb. Toward Kita-Kogane, the temple of Hondo-ji, founded in 1277, is famous as an "hydrangea temple," its grounds turning blue and violet in June and flaming red in autumn, with several nationally important documents and a medieval bell among its treasures.

• Forest and Park of the 21st Century, with the reconstructed pit dwelling beside the museum.
• Tojo-tei, the Tokugawa Akitake residence, an Important Cultural Property near Matsudo Station.
• Hondo-ji, the hydrangea and maple temple near Kita-Kogane Station.