How did they transport large stones and heavy materials for building their megaliths and large timbers for building structures?

Sakuramachi iseki, Fukuyamaken Oyabe city Middle Jomon, 4000 years bp

The Jomon through Yayoi people used a unique Y-shaped shura which allowed them to transport heavy and large items such as timbers, trees or megalithic stone.

OZAWA, Yasumi Usage of Y-Shaped Lumber of Excavations in Sakuramachi-Site (The positioning of Y-shaped lumber in the history of sledges in Japan)  Nihon Kikai Gakkai Nenji Taikai Koen Ronbunshu,VOL.2006;NO.Vol.5;PAGE.369-370(2006)

Abstract:

They had also developed a sophisticated technology involving a Y-shaped shura used for transporting heavy and/or large items such as timbers, trees or megalithic stone. Abstract: The Y-shaped lumbers of the chestnut trees were excavated at the Sakuramachi-Site in Oyabe City, Toyama, Japan in 1997. It is thought that the people of the Jomon period about 4000 years ago used the Y-shaped lumbers to transport heavy items such as giant trees. The positioning of Y-shaped lumbers in the history of sledges in Japan is discussed in this paper. The Y-shaped lumbers of the Sakuramachi-Site were compared with sledges excavated in Kitoragawa-Site of the Yayoi period in Higashiosaka City, Osaka Prefecture, Japan. It was confirmed that the Y-shaped lumbers of the Sakuramachi-Site is the oldest Shura in the world for the transportation of giant trees under the assumption that the Y-shaped lumbers at the Sakuramachi-Site are Shura