Zenpō-kōen-fun

are a special kind of Kofun. They are for high status people and very large. They have a round and a rectangular part that together look like a keyhole.https://kimotsuki-town.jp/material/files/group/67/tukazakiannaiban2.pdfhttps://www.researchgate.net/publication/359546920_Japanese_Kofun_in_Maps_given_by_a_Spaceborne_Digital_Elevation_Model_based_on_Multiple_Satellite_Data_Sets
They are sometimes called Keyhole-shaped tumuli, but that term is also used for Zenpō-kōhō-fun.

There are many types of Kofun including Zenpō-kōen-fun and Zenpō-kōhō-fun and Round Kofun and Square Kofun  

References

Category:Zenpō-kōen-fun
Category:KofunCategory:Kofun