The Keyhole-Shaped Tumulus at the Heart of the Cluster
The most prominent tomb is Tumulus No. 8, located near the summit of the hill. This keyhole-shaped burial mound measures approximately 32–33 meters in total length. Its circular rear section is about 19 meters in diameter and approximately 2 meters high, making it one of the largest burial mounds of its type in the Oki Islands.
The mound remains relatively well preserved, and a flat stone believed to have once served as a stone covering for the burial chamber can still be seen exposed near the top.
Keyhole-shaped tumuli are generally associated with powerful leaders during Japan’s Kofun period. Tumulus No. 8 is therefore thought to have been the central and earliest tomb of the cluster, possibly marking the burial of a local leader who held considerable influence in ancient Oki.
The Circular Tumuli and Ancient Burial Customs
The 14 circular burial mounds are distributed around the keyhole-shaped tomb. Many measure approximately 10–15 meters in diameter and about 1 meter in height, with several forming small groups of three or four mounds.
Most of these tombs have not been excavated, but their structures are believed to have contained horizontal stone burial chambers. Based on archaeological evidence, they are generally thought to date from around the late 6th century.
Artifacts from the Lost Tumulus No. 3
Tumulus No. 3 no longer survives, having been removed when a bull-sumo arena was constructed. Before its disappearance, however, archaeological investigations recovered objects including a Japanese sword and Sue ware pottery.
These artifacts provide valuable clues about burial customs, technology, and the material culture of the people who lived in Oki during the Kofun period. Although the physical mound has been lost, the archaeological records remain important evidence for understanding the region’s ancient history.
A Landscape Rich in Ancient Burial Mounds
The area surrounding the Tamawakasu-no-Mikoto Shrine Tumulus Cluster contains several other groups of ancient tombs, including the Kokubugahara Tumulus Cluster and the Saikyodani Tumulus Cluster. Particularly notable are tombs dating from the 5th century, suggesting that this region was an important center of political and cultural activity in ancient Oki.
The concentration of burial mounds around Tamawakasu-no-Mikoto Shrine provides an intriguing connection between the ancient political landscape and the religious traditions that continued to develop here. The tumuli may have belonged to influential families who played a major role in the administration and religious life of the islands.
Tamawakasu-no-Mikoto Shrine at the Foot of the Hills
At the southeastern foot of the tumulus cluster stands Tamawakasu-no-Mikoto Shrine, one of the most important sacred sites in the Oki Islands. The shrine enshrines Tamawakasu-no-Mikoto, a deity traditionally associated with the development and settlement of Oki, and has long served as a major center of local worship.
The Historic Soja of Oki Province
Tamawakasu-no-Mikoto Shrine is an ancient Shikinaisha, a shrine listed in the Engishiki, a major compilation of Japanese laws and religious regulations completed in the early 10th century.
In ancient times, the shrine served as the Soja of Oki Province. A Soja was a shrine where the deities of an entire province were collectively worshipped by the provincial government. Such shrines were generally established close to provincial administrative centers, reflecting the close relationship between government and religion in ancient Japan.
The exact date of the shrine’s foundation remains unknown. Various traditions associate its origins with an imperial order from Emperor Tenmu or with legends concerning a son of Emperor Keiko, adding layers of mythology and historical tradition to the site.
Oki-zukuri: A Distinctive Shrine Architecture
The present main sanctuary was constructed in 1793 and is designated an Important Cultural Property of Japan. Its thatched roof, projecting chigi finials, and rows of katsuogi give the building a dignified appearance that blends naturally with its forested surroundings.
The sanctuary is a distinctive example of Oki-zukuri, a local architectural style incorporating elements associated with Izumo Taisha’s Taisha-zukuri, Ise Jingu’s Shinmei-zukuri, and Kasuga Taisha’s Kasuga-zukuri.
Another distinctive feature is the horizontal timber known as suzume-odori, placed across the upper part of the roof structure. These architectural details make the shrine particularly interesting for visitors interested in the diversity of traditional Japanese shrine architecture.
Yaosugi: The Legendary Sacred Cedar
One of the most impressive sights within the shrine grounds is Yaosugi, a giant sacred cedar believed to be more than 1,000 years old, with some traditions placing its age at over 2,000 years.
The tree is associated with the legend of Yao Bikuni, a mysterious woman said to have lived for many centuries. Local tradition also tells of a great serpent that once lived beneath the tree’s roots.
Its enormous, partially hollow trunk and ancient appearance create an especially mysterious atmosphere. Standing beside Yaosugi offers a powerful sense of the continuity between Oki’s natural environment and its long-standing spiritual traditions.
Goryō-e Furyū: A Dramatic Traditional Festival
Every year on June 5, Tamawakasu-no-Mikoto Shrine hosts its major annual festival, Goryō-e Furyū, one of the most distinctive traditional events in the Oki Islands.
One of the most spectacular moments is the Umaire ritual, when horses charge energetically up the narrow approach to the shrine. The powerful scene combines ritual, horsemanship, and centuries-old local tradition.
Goryō-e Furyū has been designated an Intangible Folk Cultural Property of Shimane Prefecture and continues to be carefully passed down by the local community.
Oki Family Residence and Valuable Cultural Heritage
Adjacent to the shrine is the Oki Family Residence, the historic home of the family that served as hereditary chief priests of Tamawakasu-no-Mikoto Shrine. Built in 1801, the large thatched residence is an important example of traditional architecture in the Oki Islands and is designated an Important Cultural Property of Japan.
The house includes distinctive spaces associated with its religious role, including the Shinzen-no-ma, where a household Shinto altar was enshrined, and the Misogi-beya, a room associated with ritual purification.
The adjoining treasure hall preserves exceptionally valuable historical objects, including an ancient eki-rei station bell and the Okiso-in seal. These artifacts provide rare evidence of the transportation and administrative systems of ancient Japan and help demonstrate Oki’s connection with the wider Japanese state.
Walking Through the Ancient Landscape of Oki
The Tamawakasu-no-Mikoto Shrine Tumulus Cluster and the shrine at the foot of the hills together create a fascinating historical landscape spanning many centuries. The burial mounds reveal the presence of powerful communities during the Kofun period, while the shrine preserves traditions of worship that continued long after those ancient leaders were buried.
Visitors can explore the quiet hillside, imagine the people who built these tombs more than a thousand years ago, and then descend toward the shrine to encounter its traditional architecture, sacred cedar, festivals, and historic priestly residence.
Because the site can be reached from Saigo Port by bus, with the Tamawakasu-no-Mikoto Shrine-mae stop located nearby, it is a convenient destination for combining archaeology, Shinto culture, traditional architecture, and the natural scenery of Dogo Island.
For travelers seeking to understand the deeper history of the Oki Islands, this is a place where ancient burial mounds, sacred traditions, historic architecture, and the living culture of the island come together in one remarkable landscape.