The Sannai-Maruyama special historical site features the remains of a large, long-term settlement that from the Early to the Middle Jomon period (from approximately 5,500 to 4,000 years ago). Excavation that started in 1992, and pit-dwellings, large pit-dwellings, burial pits for adults, burial jars for children, mounds, the remains of large and regular-sized pillar-supported building, storage pits, clay mining pits, and remains of roads have been found. These findings have revealed how people lived in this settlement, as well as the natural environment at that time.
Other excavated items include a large number of pottery, stone artifacts, clay figures, earthenware, stoneware, woodenware such as digging sticks, lacquerware, bone tools, woven baskets called “Jomon pochettes” and woven clothes from the Jomon period. The excavation has also revealed that jade and obsidian had been brought in from far off regions.
The site was designated as a special historical site by the Japanese government in November 2000.