Kasori Shell Mound One of Japan's Largest Jomon Ring Settlements

How Kasori Shell Mound compares with familiar Chiba destinations

Kasori Shell Mound (加曽利貝塚) sits in Sakuragi 8-chome, Wakaba Ward, Chiba City. Rather than a single museum display, the site is an archaeological landscape: an extensive Jomon-period settlement whose visible remains and stratified deposits cover a scale few other local attractions match. It is managed as Kasori Shell Mound Park and hosts the Chiba City Kasori Shell Mound Museum; the site is officially designated both a Historic Site of Japan and, since October 13, 2017, a Special Historic Site — the first shell midden to receive that status.

Site layout and scale: twin rings and a figure-eight

The archaeological deposits sit on a tongue-shaped plateau on the river’s right bank about 2 kilometres upstream along a tributary of the east–west river that runs through Chiba City. The plateau measures roughly 500 metres east–west by 800 metres north–south. The shell-bearing strata along the eastern rim extend about 300 metres east–west and 400 metres north–south.

Kasori comprises two large, linked shell-mound settlements. The northern mound is an almost complete ring about 130 metres in diameter; the southern mound is a horseshoe-shaped midden with a long axis of about 170 metres. Together they form a figure-eight pattern (a double-ring settlement). The total protected area is roughly 13.4 hectares, making Kasori one of the largest shell middens in the world and one of Japan’s most important Jomon archaeological sites.

When the mounds were built: Jomon chronology and pottery types

Archaeological work at Kasori has produced a detailed chronological sequence. House remains dating to roughly 7,000 years ago have been found on the site, but the great shell mounds themselves began to be built about 5,000 years ago during the middle Jomon period. The North shell mound was constructed in the middle Jomon (approximately 5,000–4,000 years ago). At first small middens and dwellings stood on the plateau; over about a millennium the repeated disposal of shells, pottery and other refuse formed a thick “waste band” that eventually produced the ring-shaped North mound.

The North mound fell out of use before the South mound was created. The South shell mound belongs to the late Jomon period (approximately 4,000–3,000 years ago) and was formed over another span of roughly 1,000 years into a long horseshoe-shaped midden. Pottery recovered at specific excavation points has become chronologically important: pottery from point E in the North mound is classified as the Kasori E style, a marker for the latter half of the middle Jomon, while pottery from point B in the South mound is classified as the Kasori B style, a marker for the latter half of the late Jomon. These Kasori styles serve as reference types in regional Jomon chronology.

What excavations have revealed: dwellings, burials and recent work

Excavations around the two main mounds have shown a wide distribution of small mid-Jomon shell middens and dwelling traces. Finds include pottery, stone tools and animal bones recovered and displayed by the museum. Notably, in the South mound the presence of dog bones buried together with human remains was confirmed and drew public attention.

Fieldwork continued into the 21st century: in fiscal 2024 the North mound underwent its first excavation in 57 years. That work uncovered dwelling remains and artifacts dated to the late Jomon (about 4,000–3,000 years ago); media reports from the excavation stated these finds could push the date of human habitation at the North mound later than previously held chronologies.

Preservation, museum history and public programmes

Kasori entered the scholarly record in 1887 when Ueda Eikichi first introduced it. A 1907 survey by the Tokyo Anthropological Society identified Kasori as a foremost shell-mound site in Japan. Modern preservation began after the early 1960s: in about 1963 industrial land clearance by a private company destroyed part of the South mound, which provoked a preservation movement led by a local high-school teacher active in archaeology and supported by wide public sympathy.

Chiba City moved to protect the site, purchasing more than five hectares of the North mound on March 18, 1964, and developing it as a park. The Chiba City Kasori Shell Mound Museum opened on November 24, 1966, to display pottery, stone tools and animal bones excavated from the site. In 1973 the museum was one of the locations visited by Emperor Shōwa during the prefectural events for the 28th National Athletic Meet. On March 22, 1971 the North mound was designated a national Historic Site under the name “Kasori Shell Mound”; the South mound was added in 1977 so that nearly the entire shell-midden complex became protected. The October 13, 2017 designation upgraded the site to National Special Historic Site status — the first shell mound to receive that distinction.

The museum and park have also experienced controversy and change: in 1977 a group of junior-high students stole more than 160 items from the museum and exchanged them with antique dealers, an incident that affected other institutions as well. The city has run regular public programmes; events that let participants experience aspects of Jomon-period life are held frequently on the site.

Museum redevelopment and access

Because the museum building aged and the site became part of a Special Historic Site, plans were made to remove the old structure and relocate the museum about 400 metres to the northeast, on the former Ogura purification centre site. In 2022 the city announced a redevelopment plan with an initial total project cost of about 5 billion yen and a tentative reopening in fiscal 2027; the new building was expected to consider changing to a paid admission model. A 2023 procurement round produced no qualified bidders and bidding was cancelled. The city prepared a new procurement for 2025 and revised the project scale; the relocation and reopening schedule moved to fiscal 2030 (2030–2031). Following that process, in January 2026 a group led by Maeda Construction won the construction contract with a bid of 11,076,000,000 yen (tax excluded).

Practical access to the park is straightforward: the nearest station is Sakuragi Station on Chiba Urban Monorail Line 2; that station carries the secondary station name “Kasori Shell Mound” and the walk from the station to the site is about 15 minutes.

FAQ

Where is Kasori Shell Mound located?

In Sakuragi 8-chome, Wakaba Ward, Chiba City, Chiba Prefecture.

Is Kasori Shell Mound protected?

The north shell mound was designated a national Historic Site on March 22, 1971; the south shell mound was added in 1977; the site was designated a National Special Historic Site on October 13, 2017.

What is the nearest station and how far is the walk?

Sakuragi Station on Chiba Urban Monorail Line 2 (the station carries the substation name "Kasori Shell Mound") is about a 15-minute walk.