The Kofun period (approx. mid-3rd century-late 6th century) saw the rapid development of the ancient burial mounds (kofun) which is believed to have evolved from the Yayoi period (300 BCE–300 CE), where burial in designated areas where terrain was elevated became custom. It is believed that kofun-style burial mounds, with raised ground and a keyhole shape, became common in the 3rd century. It has also been suggested that certain characteristics are prevalent in preexisting tombs found on the Korean peninsula. The earliest recorded history of the imperial family of Japan is believed to date back to the 8th century.
The history surrounding kofun during the period between the 3rd and 6th century is unknown, but it is believed that rulers called okimi, an honorific title given to princes and princesses, were buried in enormous kofun during this time. It is suggested that okimi shared a connection with the establishment of Japan’s imperial family.