Man'yōgana and Inariyama sword

Man'yōgana (万葉仮名^?) is an ancient writing system that employs Chinese characters to represent the Japanese language. The date of the earliest usage of this type of kana is not clear, but it was in use since at least the mid seventh century. The name "man'yōgana" is from the Man'yōshū, a Japanese poetry anthology from the Nara period written in man'yōgana.

Man'yōgana	之乎路可良	多太古要久礼婆	波久比能海	安佐奈藝思多理	船梶母我毛
Katakana	シヲヂカラ	タダコエクレバ	ハクヒノウミ	アサナギシタリ	フネカヂモガモ
Modern	志雄路から	ただ越え来れば	羽咋の海	朝凪したり	船梶もがも
Romanized	Shiojikara	Tadakoekureba	Hakuhinoumi	Asanagishitari	Funekajimogamo

 
A possible oldest example of Man'yōgana is the iron Inariyama Sword that was excavated at the Inariyama Kofun in 1968. In 1978, X-ray analysis revealed a gold-inlaid inscription consisting of more than 115 Chinese characters and this text, written in Chinese, included Japanese personal names which were supposedly phonetically written. 

The iron Inariyama burial-mound sword (稲荷山古墳出土鉄剣 inariyama kofun shutsudo tekken^?) or kinsakumei tekken (金錯銘鉄剣^?) was excavated at the Inariyama Kofun in 1968. Inariyama Kofun is located in Saitama Prefecture. In 1978, X-ray analysis revealed a gold-inlaid inscription that comprises more than 115 Chinese characters. This sword was described as the discovery of the century for the study of ancient-Japanese history. The sword is designated a national treasure of Japan.

Read the inscription