What a keyhole-shaped kofun is
A keyhole-shaped kofun, zenpo-koenfun in Japanese, is a burial mound of the Kofun period whose plan joins a round rear mound to a squared front mound. The World Heritage nomination dossier for the Mozu-Furuichi Kofun Group describes it as a round and a square mound combined into a keyhole plan, with the principal burial in the round part. The front mound is widely thought to have been a stage for funerary ritual, and sometimes holds a secondary burial.
The front part changed over time. According to the same dossier, it was at first lower and narrower than the round part and grew gradually taller and wider in later periods. Large examples were built up in terraces, with a projecting platform at the waist where the two parts meet and a moat around the whole.
Other kofun forms include the scallop-shaped mound with a short front part, round mounds and square mounds. The square-rear form, zenpo-koho-fun, sounds similar but is a different type. The Mozu-Furuichi group gathers four forms around keyhole mounds such as the tomb attributed to Emperor Nintoku, about 500 m long.
How the records describe them
Descriptions of Historic Sites usually give figures: overall length, diameter of the round part, length and width of the front part, and whether the mound was terraced or faced with stones. Jinbayama Kofun in Shimonoseki, Yamaguchi Prefecture, is 74 m long with a round part 46 m across built in three terraces, and a short front part about half as wide as that diameter. A narrow front part matches the early form described in the dossier, and the description places this mound as the oldest in its area.
The Nagara-Sakurayama Kofun Group, straddling Zushi and Hayama in Kanagawa Prefecture, consists of two large keyhole mounds. Mound 1 is 90 m long with a round part 51 m across; mound 2 is about 88 m. Both are thought to date from around the fourth century.
On site, the outline is easier to grasp from around the mound than from on top of it: find the rise of the round part, the direction of the front part, and the narrowing waist between them. In writing, give the recorded length and diameter rather than relying on words like huge or keyhole to convey scale.
References
- World Heritage nomination dossier summary, Mozu-Furuichi Kofun Group (Japanese, Cultural Heritage Online)
- https://bunka.nii.ac.jp/docs/special_content/recommendation/19_mozu_furuichi.pdf
- Cultural Heritage Online (Agency for Cultural Affairs): Jinbayama Kofun
- https://online.bunka.go.jp/heritages/detail/162258
- Cultural Heritage Online (Agency for Cultural Affairs): Nagara-Sakurayama Kofun Group
- https://online.bunka.go.jp/heritages/detail/192582
Last verified: 2026.10.04