| Location | Osaka Pref. |
|---|---|
| Shape | Keyhole-shaped mound |
| Mound length | 94 m |
| Period | Late 4th c. |
National Historic Site notable for yielding more than 27 bronze mirrors, including numerous triangular-rimmed deity-beast mirrors. A late-4th-century keyhole mound (94m) with a dual vertical stone-cist structure. The discovery of a mirror inscribed "Keishi Year 3" (239 CE) has prompted discussion of links to Himiko and Yamatai. Internationally known for its relevance to the "mirrors of Himiko" debate—one of the greatest mysteries of ancient Japanese history. The name "Koganduka" (Golden Mound) derives from a tradition that brilliant grave goods were found here. More than 500 triangular-rimmed mirrors have been found in Japan but none in China, sustaining a lively dispute between "Japanese-made" and "Wei gift" theories.
Two burial chambers (vertical stone cists) — one each in the rear circle and front section (dual-chamber structure). Finds: 27+ bronze mirrors including a "Keishi Year 3 (239 CE)"-inscribed triangular-rimmed deity-beast mirror, additional triangular-rimmed mirrors, pictorial deity-beast mirrors, iron swords, iron arrowheads, and beads. The 239 CE inscription coincides with the year Himiko sent tribute to Wei as recorded in the Wei Zhi, making this mirror a key reference in the ongoing "Wei gift" vs "Japanese-made" debate. Finds held at the Osaka Prefectural Museum of Yayoi Culture and the Tokyo National Museum. National Historic Site (1981).
The excavated mirrors are held at the Osaka Prefectural Museum of Yayoi Culture (within Izumi City) and the Tokyo National Museum, with some on permanent display. The site is preserved in Izumi City and can be viewed by walking around the perimeter.