Before this mirror was discovered, the oldest ancient mirror had been the mirror with the year inscribed as 'Sekiu Gannen' (first year of Sekiu, or 238) (Sekiu, or Chiwu is the name of the era of the Emperor Da Di of Wu Dynasty of China) which was excavated from Toriibara Kitsunezuka-kofun Tumulus in Ichikawa Misato Town in Yamanashi Prefecture.
これまでは山梨県市川三郷町の鳥居原狐塚古墳出土の紀年銘鏡「赤烏元年」（呉の大帝の年号で238年）が最も古かった。