The Arashima Kofun Cluster (荒島古墳群) is a group of burial mounds dating from the late Yayoi period through the Kofun period, situated on the Arashima Hills in the Aratori‑cho and Kujira‑cho neighborhoods of Yasugi, Shimane Prefecture, Japan. The site lies in the San'in region, overlooking Nakaumi (Lake Nakaumi).
Designation
The cluster was designated a National Historic Site of Japan in 1936. In 1999 the protected area was expanded to encompass additional tumuli, and the site is now officially referred to as the Arashima Kofun Cluster.
Composition
The complex comprises several distinct groups of tumuli:
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Taisei Kofun – a large rectangular (hōfun‑style) mound discovered in 1911, measuring approximately 60 m on each side and 6 m in height. Excavations revealed a pit‑style stone burial chamber containing a triangular‑rimmed bronze mirror, an iron sword with a ring‑shaped head, Haji ware pottery, and other grave goods.
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Tsukuriyama Tumuli – located on the western side of the hills, this group includes four burial mounds. Notable examples are:
- Tsukuriyama Kofun No. 1, a square tumulus about 60 m per side and 7 m high, with two pit‑style stone chambers. Artifacts recovered include bronze mirrors (triangular‑rimmed and square‑shaped), a spindle‑shaped stone object, glass beads, and iron swords.
- Tsukuriyama Kofun No. 3, measuring 38 × 36 m, excavated in 1960, yielding a bronze mirror depicting deities and beasts, jasper and glass beads, an iron sword, and a spear.
- Tsukuriyama Kofun No. 5, situated outside the nationally protected boundaries, is another rectangular mound of the early Kofun period.
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Shiotsuyama Tumuli – on the eastern side, eleven tumuli have been confirmed. Highlights include:
- Shiotsuyama No. 1, a large “four‑corner protruding” (四隅突出形) mound characteristic of the late Yayoi period, featuring a square core with polygonal extensions at each corner—a style found in the Kibi, San'in, and San’yō regions.
- Shiotsuyama No. 6 and No. 10, early Kofun‑period rectangular tombs retaining the four‑cornered shape, among the largest of this type in the area.
The Shiotsuyama group was not fully recognized until archaeological surveys in the late 1970s. During construction of the San’in Expressway, a tunnel was built beneath Shiotsuyama No. 1 to preserve the mound.
Historical Significance
The cluster provides important evidence for the evolution of tumulus construction in the Izumo region, illustrating the transition from Yayoi‑period burial practices to the more elaborate forms of the Kofun period. The variety of mound shapes—square, rectangular, and the distinctive four‑corner protruding style—reflects regional adaptations and social differentiation during this transformative era.
Access and Preservation
The site is maintained by Yasugi City as a historical park known as “Ancient Izumo Royal Mausoleum Hill.” It is accessible on foot within approximately 15 minutes from Arashima Station on the JR West San’in Main Line. No visitor facilities are present on the tumuli themselves.
References
Information summarized from the English Wikipedia entry on the Arashima Kofun Cluster, which draws on publications by the Agency for Cultural Affairs of Japan and the National Historic Site Encyclopedia (Isomura & Sakai, 2012).