Researchers have identified an intricate inlaid gold pattern on an iron spear inserted into a gilt bronze sheath, unearthed decades ago on the Okinoshima sacred island off the coast of Munakata, Fukuoka Prefecture, Japan. It is the first known instance of a gold-inlaid spear in East Asia and provides valuable insight into the ceremonial practices of the Yamato Dynasty during the late Kofun period.

Gilt bronze spear sheath containing iron spear. Credit: Preservation and Utilization Council of “Sacred Island of Okinoshima and ᴀssociated Sites in the Munakata Region”

Originally found in 1954 beneath one of the island’s mᴀssive sacred rocks, the artifact had lain relatively unanalyzed for many years until Japan’s Cultural Affairs Agency began a project to digitally examine over 4,200 of Okinoshima’s metal artifacts using X-rays and CT scans. The spear was discovered as part of an offering at the Okitsu-gū Shinto shrine, which occupies the entire island — a site that hosted state rites from the 4th to the 9th century AD to honor sea deities and safeguard maritime journeys.

The spear itself is believed to have been produced in Japan in the late 6th to early 7th century, with stylistic and metallurgical influences from the Korean Peninsula. The weapon, measuring approximately 30 centimeters in length and still lodged in its sheath, revealed decorative designs completely covering its surface when examined through X-ray and CT imaging. The patterns, covered for centuries by corrosion, most likely feature a combination of stylized phoenix motifs, tortoise-shell designs, arabesque decorations, and possibly flower or feather elements.

X-ray transmission pH๏τograph. Credit: Gangoji Insтιтute for Research of Cultural Property / Preservation and Utilization Council of “Sacred Island of Okinoshima and ᴀssociated Sites in the Munakata Region”

According to the authorities at Munakata Taisha shrine, the craftsmanship involved a technique known as kinzōgan, a forging method in which gold or another metal is embedded into carved lines. Though the exact composition of the inserted material is still under analysis, gold is the leading candidate.

3D model created by X-ray CT. Credit: Gangoji Insтιтute for Research of Cultural Property / Preservation and Utilization Council of “Sacred Island of Okinoshima and ᴀssociated Sites in the Munakata Region”

The spear was not made for combat. The ornamentation and fragile construction indicate that it was a votive item, purposely made as an offering to the island’s deity. Researchers note that the find underscores the level of artistic and religious investment the Yamato state placed in its religious observances.

Designated a World Heritage Site, Okinoshima remains one of Japan’s most revered sacred locations. The entire island is considered to be a kami (god) in the Shinto belief. Women are forbidden from setting foot on its soil to this day, and men may only visit after strict purification rituals. More than 80,000 objects have been unearthed from the island, all of which have been classified as national treasures by the Japanese government.

More information: Preservation and Utilization Council of “Sacred Island of Okinoshima and ᴀssociated Sites in the Munakata Region”