Shinpukuji Shell Mound

A Ring of Shells on the Omiya Upland

Shinpukuji Shell Mound is a Jomon settlement site of the late and final Jomon periods at Jonan and Shinpukuji in Iwatsuki Ward, Saitama City, Saitama Prefecture, designated a national Historic Site on 19 July 1975. It dates from roughly 3,800 to 2,600 years ago. The site occupies the Iwatsuki spur of the Omiya upland at 10 to 13 metres above sea level, and measures about 160 metres east to west and 180 metres north to south.

It has two parts. On the flat ground above, shells lie in a ring about 150 metres across. To the west, where the land drops into a small side valley of the Ayase River, a peat layer site extends across the wetland. Shinpukuji Shell Mound has been known to archaeologists for a century because both survive together as one site.

Why It Was Designated

Excavation here goes back to 1926. Pottery and stone tools came out, and so did wooden objects, which is unusual enough to have kept archaeologists returning. In 1934 a pottery type named after this site, the Shinpukuji peat layer type, was proposed, and it became a yardstick for dating the first half of the final Jomon period across the Kanto region.

The Historic Site designation was made on 19 July 1975. Seven further additions to the designated area followed between 1990 and 2020, widening the protected ground in stages. Ownership today is split between Saitama City and private individuals.

Shells and Peat

The range of shells is wide. In Saitama City's tabulation the dominant species is the brackish-water Yamato clam, with saltwater species such as oysters, blood cockles, hard clams and trough shells also common, alongside freshwater pond snails and freshwater mussels. A borehole survey of the valley in 2002 found, through diatom analysis, that the area had been a freshwater environment before the settlement was established. The shells tell a different story from the sediment.

The peat layer in the wetland stayed waterlogged, and waterlogged ground preserves plant material. Wooden objects and seeds that would have rotted away on the upland survive here: chestnut, walnut, horse chestnut and melon among them, evidence of what the people of this settlement gathered and ate.

In June 2023 Saitama City began excavating the peat layer itself. It is only the second such excavation at a nationally designated Historic Site in Japan, after the Korekawa Nakai site in Hachinohe, Aomori Prefecture. The work continues, and the city's cultural properties division publishes results as they come.

The Owl Figurine

The best known find from Shinpukuji Shell Mound is the mimizuku dogu, a clay figurine whose face resembles a horned owl and which takes its name from the bird. Eyes and mouth are made from discs of clay applied to the surface, and the ears carry earrings. It is designated an Important Cultural Property and is held by the Tokyo National Museum.

It is not the only one. In 2020 another owl figurine came out of the western part of the site, showing that this form was made here more than once. Clay tablets, clay earrings, curved beads and stone swords have also been recovered.

Visiting

Shinpukuji Shell Mound is an open site with no opening hours and no admission fee. The shell layer lies underground, so what is visible from the surface is the shape of the land itself: the flat of the upland and the fall towards the wetland along the Ayase River. Why people settled at this particular point has to be read from that topography.

The designated land is divided between Saitama City and private owners, and some of it is private property. The city asks visitors not to inconvenience owners, site managers, neighbours or other visitors. There is no car park for visitors and no interpretive building at the site.

Saitama City holds open days at the excavation, announced on the cultural properties division's pages. That is the reliable way to see finds and work in progress. Enquiries go to the Cultural Properties Protection Division of the Saitama City Board of Education, on 048-829-1723.

The nearest station is Iwatsuki on the Tobu Urban Park Line, with the site lying east of it. The usual approach is to change at Omiya onto the Tobu Urban Park Line.