While the early Jōmon period (approx. 5,000 years ago) was the warmest, it gradually became cooler during the middle and late periods, which made it more difficult to gather food. The big villages that had flourished until the middle period became smaller and the villages became more dispersed. As such, it became necessary to strengthen connections with relations living far away. Gigantic institutions like stone circles, embankment circles, and wood circles were built with the aim of reaffirming the spiritual connections between the people building and using them as well as increasing their collective awareness in daily life.