An observation establishing the time period was taken from a small segment of Emperor Yuryaku's rule, as indicated in artifacts and historical logs: The written letters inscribed on the iron sword, which was excavated from Inariyama-kofun Tumulus in Gyoda City, Saitama Prefecture: The written letters inscribed on the long sword, which was excavated from the Eta Funayama Tumulus in Tamana City, Kumamoto Prefecture.
埼玉県行田市稲荷山古墳から出土した鉄剣銘や熊本県玉名市江田船山古墳から出土した大刀銘から雄略天皇の治世の一端が分かる。