古墳Mozu Kofun Group (Daisen Kofun) · 6 min read
Keyhole Tombs: What Are Japan's Kofun — and Who Rests Inside?
Japan's giant keyhole-shaped tombs, the 486-meter Daisen Kofun in Osaka, and the best free place to see its shape from above.
✓ Fact-checked 2026-11-08 · how we check
文A Summary in your language
日本語
古墳は3〜7世紀を中心に築かれた支配者の墓。大山古墳は全長486mで日本最大、仁徳天皇陵として宮内庁が管理し、中には入れません。鍵穴の形は地上からは見えないので、堺市役所21階の展望ロビーから眺めます。
繁體中文
古墳是主要建於 3 至 7 世紀的統治者陵墓。大山古墳全長 486 公尺，為日本最大，由宮內廳作為仁德天皇陵管理，不可進入。鑰匙孔形狀從地面看不到，可從堺市役所 21 樓展望大廳眺望。
简体中文
古坟是主要建于 3 至 7 世纪的统治者陵墓。大山古坟全长 486 米，为日本最大，由宫内厅作为仁德天皇陵管理，不可进入。钥匙孔形状从地面看不到，可从堺市役所 21 楼展望大厅眺望。
한국어
고분은 주로 3~7세기에 축조된 지배자의 무덤입니다. 다이센 고분은 길이 486m로 일본 최대이며, 닌토쿠 천황릉으로 궁내청이 관리해 들어갈 수 없습니다. 열쇠구멍 모양은 지상에서 보이지 않아 사카이 시청 21층 전망 로비에서 바라봅니다.
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Quick answer
Kofun are ancient burial mounds built for Japan's rulers and elites, mostly between the 3rd and 7th centuries. The biggest, Daisen Kofun in Sakai, Osaka, is 486 meters long — one of the largest tombs in the world. It is cared for as the tomb of Emperor Nintoku, and you can't go inside — but you can see its keyhole shape from above.
一A forest shaped like a keyhole
From the ground, Daisen Kofun looks like a huge wooded hill surrounded by water. From the sky, it becomes a perfect keyhole: a round mound joined to a square one, wrapped in three moats.
| Length | Height | |
|---|---|---|
| Daisen Kofun, Japan | 486 m | 35.8 m |
| Great Pyramid of Giza | 230 m | 146 m |
It is lower than the pyramid, but longer from end to end. Japan has around 160,000 burial mounds in total; Daisen is the largest.
二Who rests inside?
The Imperial Household Agency cares for Daisen Kofun as the tomb of Emperor Nintoku, and many people in Japan call it Nintoku-tennō-ryō.
Historians still discuss who exactly was buried in each of the great kofun, because the burial chambers have never been scientifically excavated. The mounds are treated as sacred resting places of the imperial ancestors, so entry is not permitted.
You can still pay your respects: there is a place of worship facing the front of the tomb, with a torii.
三World Heritage since 2019
In July 2019, UNESCO listed 49 kofun in southern Osaka as the Mozu-Furuichi Kofun Group — 23 in the Mozu area around Sakai and 26 in the Furuichi area. It was Osaka Prefecture's first World Heritage Site. Most of these mounds were built from the late 4th to the late 5th century.
Look for it: the slopes of these mounds were once lined with haniwa — clay cylinders and figures of people, animals and houses. At the Sakai City Museum, look for haniwa found in the Mozu area.
四Where to see the keyhole
The best free view is from the observation lobby on the 21st floor of Sakai City Hall, about 80 meters up, a short walk from Sakai-higashi Station. You won't see a perfect keyhole — the mound is too big — but you'll understand its size against the city.
For the full shape, the Sakai City Museum in Daisen Park shows aerial views and exhibits on the kofun. Or follow the path around the outer moat: about an hour on foot, less by rental bicycle.
探2 hidden details in the Mozu Kofun Group
Open the hunt for Mozu Kofun Group (Daisen Kofun) →
How to see it
| Where | Sakai, Osaka — near JR Mozu Station |
| Entry | Free to walk around; the mound itself is closed |
| Best view | Sakai City Hall, 21st floor (free) |
| Time needed | Half a day with the museum and cycling |
Sources
- Nippon.com: Japan Burial Site Under Excavation One of World's Largest — https://nippon.com/en/features/h00316
- Nippon.com: Ancient Burial Mounds Added to UNESCO List — https://www.nippon.com/en/japan-data/h00492/
- Japan Tourism Agency multilingual explanations: Sakai City Hall Observation Lobby
- Sakai City (official site)