The Sannai-Maruyama Site (三内丸山遺跡, Sannai-Maruyama iseki) is an archaeological site and museum located in the Maruyama and Yasuta neighborhoods to the southwest of central Aomori in Aomori Prefecture in northern Japan, containing the ruins of a very large Jōmon period settlement.

The ruins of a 40-hectare (400,000 m2; 99-acre) settlement were discovered in 1992, when Aomori Prefecture started surveying the area for a planned baseball stadium.

It is located on a 20 meter high fluvial terrace on the right bank of the Okidate River, at the tip of a ridge extending southwest from the Hakkōda Mountains.

Additionally, they stored their food in pits, which allowed them to hide it when they left the site since the occupants were still semi-nomadic.

[4] Due to its large size, it is believed that this structure could have functioned as a monument, watchtower, or a lighthouse overlooking Mutsu Bay (which was larger than at present).

Many of the post holes from these buildings overlap each other, which suggests that the structures were being rebuilt in the same location and facing the same direction.

A large amount of earthenware and stoneware were recovered from these middens, including approximately 2,000 clay figures, wood products, bones and antler objects and tools, and fragments of baskets and lacquerware.

Its abandonment was likely due to the population's subsistence economy being unable to result in sustained growth, with its end being spurred on by the reduced amount of natural resources during the neoglaciation.

[7] The presence of ruins at Sannai-Maruyama was known even during the Edo period, as travelers through the area commented in finding pottery shards and clay figurines.

Due to the large number of finds during the rescue archaeology conducted at the time, including the foundations for the large six-pillared building in June 1994, Aomori Prefecture cancelled the baseball stadium project and decided to preserve the site in August 1994 as an archaeological park.

Over this period of time, the site changed from a seasonal camp, to the home of a more mobile society, and finally to a settled village.

Evidence of this sedentary lifestyle can be found in the form of intense use of natural resources such as nuts, fish, and a wide diversity of plants, as well as changes in storage facilities.

Construction on this scale implies the existence of a coordinated labor force due to the sheer size of these posts.