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

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)…