Hikawa Bronze Swords Day

What Is Hikawa Bronze Swords Day?

Every July 12th is "Hikawa Bronze Swords Day" (ひかわ銅剣の日, Hikawa Dōken no Hi) in Shimane Prefecture. On July 12, 1984, an extraordinary archaeological discovery was made at the Kojindani site (荒神谷遺跡) in what was then Hikawa County (now Izumo City), Shimane Prefecture: 358 bronze swords were unearthed from a single site — the largest collection of bronze swords ever discovered in one location in Japan. The find transformed scholarly understanding of the Yayoi period (300 BCE – 300 CE) and the ancient culture of the Izumo region.

The Discovery at Kojindani

The Kojindani bronze swords were discovered during a routine irrigation ditch survey by the Shimane Prefecture Board of Education. Excavators initially uncovered a single sword, then more, and more — until 358 swords had been systematically uncovered from a carefully arranged deposit. The swords were all of the same Yayoi-period style and had been deliberately arranged in rows and buried — not randomly discarded, but intentionally cached. The scale of the find was unprecedented: until Kojindani, the total number of bronze swords recovered from all sites in Japan combined was fewer than 300.

More Discoveries at Kojindani

The initial 358-sword discovery was followed the next year (1985) by additional remarkable finds at the same site: 6 bronze bells (銅鐸, dōtaku) and 16 bronze spear tips (銅矛, dōboko) were discovered nearby. Together, these artifacts represented a ritual deposit of extraordinary magnitude. Two years later, the nearby Kamo-Iwakura site (加茂岩倉遺跡) yielded 39 dōtaku — the largest single cache of bronze bells ever found in Japan. The concentration of such spectacular finds in the Izumo region has fundamentally reshaped understanding of Yayoi-period ritual and political organization.

What the Swords Tell Us

The Kojindani bronze swords were not weapons in the conventional sense — they were ritual objects, too thin and fragile for actual combat. Their careful deposition suggests a large-scale ritual event — possibly a ceremony conducted by or for a powerful chieftain or religious leader in the Izumo region. Izumo is already significant in Japanese mythology as the home of Ōkuninushi no Mikoto, the deity associated with the Izumo Grand Shrine (出雲大社). The archaeological discoveries at Kojindani suggest that Izumo was indeed a major center of ritual power in the Yayoi period.

Fun Facts

• National Treasure: The Kojindani bronze swords are designated a National Treasure of Japan and are housed at the Shimane Museum of Ancient Izumo (島根県立古代出雲歴史博物館) in Izumo City.
• Kojindani Archaeological Site: The site itself is preserved as a National Historic Site and can be visited, with an interpretive museum explaining the excavation and its significance for understanding Yayoi-period Japan.