What is "kofun"

n. A megalithic tomb or tumulus in Japan, often with a distinctive keyhole-shaped mound.

Kofun (古墳, from Sino-Japanese "ancient grave") are megalithic tombs or tumuli in Japan, constructed between the early 3rd century and the early 7th century AD. They gave their name to the Kofun period (middle 3rd century to early-middle 6th century). Many of the Kofun have distinctive keyhole-shaped mounds , which are unique to ancient Japan. The Mozu- Furuichi kofungun or tumulus clusters have been proposed for inscription on the UNESCO World Heritage List, while Ishibutai Kofun is one of a number in Asuka-Fujiwara similarly residing on the Tentative List.