Since the waka poems of Sakimori were not contained in "Manyoshu" (Japan's oldest anthology of poems) before the eighth century, Sakimori is considered to be placed when the Kyusyu dynasty was destroyed at the end of the seventh century.
だが、『萬葉集』には8世紀以前の防人の歌は無いので、防人が置かれたのは九州王朝が滅亡した7世紀末頃と考えられる。