A prehistoric Japanese building constructed with wooden pillars that have an age range spanning 700 years

Sixteen pillars in a prehistoric building in Osaka, Japan, were precisely dated using a 4354-year-long tree-ring δ¹⁸O master chronology. The building was previously thought to have been constructed in the 1^st century BCE (i.e., the middle Yayoi Period), when the metal-working culture in the Japan archipelago expanded rapidly and large-scale agricultural settlements with large moats and agricultural rituals using bronze became prominent. Fifteen of the 16 pillars have no sapwood, and thus their felling dates cannot be determined. Despite this constraint, our analysis demonstrated that the building was constructed using pillars that yield ages from 782 to 52 BCE. Our δ¹⁸O-based dates were successfully verified by reproducing the rapid ¹⁴C increase observed at 665–663 BCE, which provides independent support for the tree-ring dating. We propose three potential explanations for the 700-year range in the pillar ages. Firstly, the outer layers of the tree trunks may have been removed prior to the construction of the building. Secondly, the Yayoi people might have utilized wood from buried trees, which could have originated from landslides occurring intermittently over extended periods of time. Thirdly, some of the pillars may have been repurposed from other structures. The pillar dated to 52 BCE, which contains complete sapwood rings, was likely logged shortly before construction of the building, whereas some of the remaining pillars may have been sourced from dead wood. Our findings suggest that the use of wood during the middle Yayoi Period was more complex than the simple harvesting of living trees.