Archaeological Evidence of the Medieval Honden
Ancient and medieval versions of Izumo Ōyashiro Shrine were said to have reached 48 meters in height, but detailed plans of the early structures are scarce. One rare exception is a diagram known as the Kanawa no gozōei sashi zu (Diagram for the Placement of Metal Rings during Shrine Construction) that has been passed down through the family of the shrine’s chief priests (kokusō).
Dating to between the thirteenth and sixteenth centuries, the diagram depicts the Honden (main sanctuary) of the time as a building supported by nine pillars arranged in a three-by-three grid. Although this design is the same as that of the current structure, the scale is much larger. In the diagram, each pillar is three meters in diameter and consists of a trio of massive logs bound together by metal bands. While the height of the structure is not given, the entrance staircase is said to be roughly 109 meters in length. For centuries, no physical evidence of such a massive structure had been found.
This changed during archaeological excavations that began in 2000. The remains of several pillars were discovered beneath the earth near the Yatsuashimon Gate, the area in front of the Honden. Three pillars were found, and the other six may still exist beneath the modern Honden and its neighboring structures. The excavated pillars include the central pillar (shin no mihashira), the front gable-end pillar (uzubashira), and the southeastern side pillar (gawabashira). The arrangement of the pillars matches the description in the Kanawa no gozōei sashi zu plan, and radiocarbon dating indicates that they were likely installed during a rebuilding of the shrine in 1248.
Visitors will notice an area of circular red tiles in the flagstone area between the Haiden (worship hall) and the Honden. These mark the places where the pillars were found, and their size accurately reflects that of the triple logs (inner red circles) that made up each pillar (outer circle). The southeastern side pillar was reburied once excavations were complete, but the central pillar and the gable-end pillar have been removed and preserved. The central pillar is on display in the Hōmotsuden (treasure hall), while the gable-end pillar can be seen at the Shimane Museum of Ancient Izumo, which neighbors the shrine.