The description of the Emperor Seimu in Kyuji (mythical tradition) of the "Kojiki and Nihonshoki" is far less than that of the other emperors, therefore, his historical existence is being suspected, but if he did exist, it might have been in the middle of the fourth century.
『記・紀』に載せる成務天皇の旧辞部分の記事は、他の天皇のそれに比して極端に文量が少なく、史実性には疑いが持たれているものの、実在を仮定すれば、その年代は4世紀半ばに当たるか。