Sannai-Maruyama in Aomori preserves one of Japan’s largest Early to Middle Jōmon settlements, occupied broadly from about 3900 to 2200 BCE. Excavations have revealed pit dwellings, storage pits, graves, roads, refuse mounds and large post-built structures. This range makes the site valuable not for a single treasure but for evidence of community organisation across many generations.
The settlement came to national attention during surveys begun in 1992 before a planned baseball stadium. The scale of discoveries led Aomori Prefecture to preserve the site. It is now a Special Historic Site and one component of the UNESCO World Heritage property Jomon Prehistoric Sites in Northern Japan, inscribed in 2021.