The most frequent type of residential structure at Sannai Maruyama is a pit dwelling. Like the thatched tipi form, the floor of a pit dwelling was dug into the ground. Then, supporting posts were placed at the corners and the walls and roof were built and roofed with thatch. The average size of a pit dwelling is between three and four meters in diameter with a 12 square meter floor plan.
The earliest pit dwellings at Sannai Maruyama were during the Early Jomon period, built between 5900 and 5400 years ago. At that time, Sannai was comparatively small and simple, a collection of pit dwellings and the beginnings of a midden (refuse dump).
See the official Sannai Maruyama website for further information. If you are planning a visit to Japan, the site is open to visitors, with a museum and several reconstructed buildings.
Habu, Junko 2008 Growth and decline in complex hunter-gatherer societies: a case study from the Jomon period Sannai Maruyama site, Japan. Antiquity 82:571–584.
Habu, Junko and Clare Fawcett 1999 Jomon archaelogy and the representation of Japanese origins. Antiquity 73:587-793.
Habu, Junko, Minkoo Kim, Mio Katayama, and Hajime Komiya 2001 Jomon subsistence-settlement systems at the Sannai Maruyama site. Bulletin of the Indo-Pacific Prehistory Association 21:9-21. Free download
Anonymous. The Sannai Maruyama Site: Extraordinarily Large Settlement in Prehistoric Japan. Undated pamphlet available at the Sannai Maruyama site webpage.