Qualla: Isohama Kofun Cluster

Isohama Kofun Cluster: Introduction

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Saigen Jiro, CC0. From the air, they look like gentle swells in an otherwise flat coastal landscape -- earthen mounds softened by seventeen centuries of rain and root growth, barely distinguishable from the surrounding terrain of the town of Oarai. But the Isohama Kofun Cluster, perched on a hill facing the Pacific Ocean about three kilometers southwest of the Naka River's mouth, is one of the most significant archaeological sites in Ibaraki Prefecture. Excavations have pulled more than 4,100 grave goods from these tumuli: bronze mirrors, iron swords, jade magatama beads, jasper tubes and balls, and miniature replicas of everyday objects meant to accompany the dead into the next world. Three of the mounds were designated a National Historic Site in 2020, with three more under consideration. What these tombs suggest is striking -- that a powerful local dynasty once controlled this stretch of the Kanto coastline, and may have maintained maritime connections all the way to the Yamato heartland of western Japan.

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Image: Saigen Jiro | CC0

Isohama Kofun Cluster: Keyhole Kings

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Saigen Jiro, CC0. The two most prominent tombs in the cluster are keyhole-shaped kofun -- that distinctive form, visible only from above, where a square platform joins a circular mound. The Hisagezuka Kofun stretches 101.4 meters in total length, making it one of the largest burial mounds in Ibara...

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Image: Saigen Jiro | CC0

Isohama Kofun Cluster: The Giant Circle

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Alexrk2, CC BY-SA 3.0. The Kurumazuka Kofun takes a different form entirely. At 88 meters in diameter, it is one of the largest circular-type kofun anywhere in Japan -- a massive round mound without the squared-off forward platform of its keyhole neighbors. Circular kofun are generally considered sligh...

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Image: Alexrk2 | CC BY-SA 3.0

Isohama Kofun Cluster: A Settlement of the Living and the Dead

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Saigen Jiro, CC0. The kofun did not stand in isolation. The surrounding Higekama Ipponmatsu site preserves traces of a large-scale settlement that stretched continuously from the preceding Yayoi period into the Kofun era, suggesting that the people who built these tombs lived right beside them for...

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Image: Saigen Jiro | CC0

Isohama Kofun Cluster: What the Earth Remembers

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Saigen Jiro, CC0. Walking the site today, just a 12-minute stroll from Oarai Station, the mounds have settled into the suburban landscape of a quiet coastal town. Grass covers the earthwork contours. Trees shade the slopes where haniwa once stood in ceremonial rows. The 4,100-plus artifacts recove...

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Image: Saigen Jiro | CC0