It would be during the middle of the fifth century, a vertically constructed stone chamber became relatively wider than a previous shape (It was used to be a long and narrow shape), which was an interior structure of a large class Kofun (ancient burial mound), and was implemented in the Kanai region; the Kofun would have been designed to house a stone coffin, shaped in the form of a large oblong chest (for clothing, personal effects, etc.).
5世紀半ばになり、畿内の大型古墳の竪穴式石室が狭長なものから幅広なものになり、長持ち型石棺を納めるようになった。