Iron sword excavated from Inariyama Kofun (gold-inlaid inscribed sword)

The Inariyama Kofun iron sword was excavated in 1968 from the rear circular mound of Inariyama Kofun in Gyoda City, Saitama Prefecture. Initially obscured by corrosion, an X-ray examination at the Saitama Prefectural Museum in 1978 revealed a gold-inlaid inscription covering both faces of the blade, a discovery widely reported that September.

The blade measures approximately 73.5 cm in length. A total of 115 Chinese characters are inlaid in gold across both sides — the front recording the genealogy of the sword's owner, the reverse recording his official rank and the name of a great king — making it the longest inscription found on any Kofun-period sword.

The inscription bears a date corresponding to a "kanoto-i" year and the name of "King Wakatakeru," stating that the owner served this king and assisted in governing the realm. King Wakatakeru is widely identified with Emperor Yuryaku, the twenty-first sovereign recorded in the Nihon Shoki, and the kanoto-i year is generally dated to 471 CE.

The same royal name appears on the silver-inlaid sword excavated from Eta Funayama Kofun in Kumamoto Prefecture, making this blade a first-rank written source demonstrating that Yamato court authority extended from Kyushu to the Kanto region in the late 5th century — a discovery of major importance for the study of ancient Japanese history.

The sword was designated an Important Cultural Property in 1981 and, together with the rest of the Inariyama Kofun finds, a National Treasure in 1983. It is now held by the Saitama Prefectural Sakitama Historical Museum in Gyoda City, displayed and stored in a nitrogen-filled case.