Keyhole tomb order
The keyhole tomb order (前方後円墳体制, zenpōkōenfun taisei) was a social order in Japan that appeared in the early Kofun period and is visible as zenpōkōenfun became standardized in that period. The concept was proposed by archaeologist Hiroshi Tsude in 1991.
Other similar concepts were proposed by other archaeologists, such as Kazuo Hirose's keyhole tomb state (前方後円墳国家, zenpōkōenfun kokka) and Yoshirō Kondō's keyhole tomb system (前方後円墳秩序, zenpōkōenfun chitsujo). These various theories express similar concepts, but the different archaeologists focus on different aspects, and there is particular conflict in terms of the development of the state.
The keyhole tomb order is believed to represent a new level of social complexity and the advent of the Yamato Kingship.