Toyohashi (Japon): Rare prehistoric shell mound suggests possible mid-Jomon shell trade
Piles of clamshells with a stone structure above them are seen at an excavation site at the Sakatsuji Shell Midden in Toyohashi, Aichi Prefecture. | CHUNICHI SHIMBUN
An ancient heap of shells at Sakatsuji Shell Midden in the city of Toyohashi, Aichi Prefecture, most likely served as a clam processing site in the latter half of the mid-Jomon Period, approximately 4,500 years ago, an investigation conducted by the city’s board of education has revealed.
While there are ruins in eastern Japan that indicate organized production during the mid-Jomon Period — including the Nakazato shell midden, or mound, which is a national historic site in Tokyo’s Kita Ward — it is extremely rare to find one in the Chubu region or further west. This latest discovery will provide important clues about the culinary lifestyle and economic activities conducted in the Jomon Period.
The Sakatsuji shell mound is one of the Muro cluster of seven shell middens in Aichi Prefecture.
An excavation conducted in the 1970s showed a rough scale of activities there, but details had remained unknown.
The mound is located approximately 3.5 km inland of what is now Mikawa Bay. But prior to the bay being filled in to create rice fields in the Edo Period the shell mound had faced the sea, along a stretch of coastland where the shores are shallow.
As a land consolidation project is scheduled to start in the area that includes the mound, the board of education had been excavating approximately 1,000 square meters of land since May.
The mound, made almost entirely of clamshells, measures roughly 1.6 meters high, about 6 meters wide and more than 24 meters long.
At least four layers have been identified, sandwiched between soil streaked with charcoal.
The team also discovered around 55 objects that looked like furnaces assembled from stones, and the members expect to find more as they continue excavating.
“We believe that the clams were boiled in the furnaces, and their meat stripped from the shells. Afterward the shells were piled up, then the ground was leveled and made into a processing site again,” said a member of the excavation team. “That kind of process must have been repeated again and again.”
The excavation team was not able to find any evidence of residences nearby, so it was likely the workers who dug and processed the clams lived in another area.
The volume of shells discovered was so huge it is hard to believe that they were consumed within the region, and the excavation team has said there is a possibility people dried the clams after they were boiled so that they would last longer and could be used for trading.
The shells are of various sizes. “We found many large shells similar to those seen in high-class Japanese restaurants. The clams must have become quite salty when boiled in sea water, so maybe they were used to make soup stock,” a member of the excavation team said. Several hundred furnaces have been found in the other six shell mounds in Muro. They share the same features as the Sakatsuji midden, which indicates the whole area was bustling with clam processing at the time.
However, the other six shell middens were from the late Jomon Period — approximately 2,300 to 3,800 years ago — which means the clam processing site of Sakatsuji was much older.
Most of the furnaces found in the other shell middens were also without stone structures, and were constructed in such a way that earthenware was placed directly on the floor.
“Perhaps they changed to a simpler furnace in order to meet the growing demand for clams,” said one of the team members.
The excavation will continue until the end of March and an on-site briefing is expected to be held in mid-February.
According to Tomonari Osada, a part-time lecturer specializing in archaeology at Chubu University, the Tokai region during the mid-Jomon Period is believed to have been less socially developed compared to the period immediately before the beginning of the Yayoi Period.
“I would be surprised if the production conducted at the Sakatsuji shell midden was for the sake of trading and distribution to other regions. We need to focus on this site and conduct further analysis to determine whether the objects made of stones were indeed furnaces for boiling (clams).”