Kinreizuka Kofun is a large keyhole-shaped burial mound located in Nagasuka, Kisarazu City, Chiba Prefecture. It forms part of the Gion-Nagasuka Kofun Tumulus Group and is one of the area’s most significant archaeological sites.
The tomb is particularly notable for the discovery of five small golden bells and a remarkable collection of other burial goods. The exceptional quality and quantity of these artifacts provide valuable insight into the status of powerful local leaders in the late Kofun period.
Kinreizuka Kofun was a large keyhole-shaped burial mound with an estimated total length of approximately 100 meters. It was formerly known as Futagozuka Kofun.
During an archaeological excavation in 1950, researchers discovered an intact horizontal stone burial chamber that had not been looted. Among the remarkable artifacts found inside were five golden bells. The discovery led to the tomb being renamed Kinreizuka Kofun, meaning roughly “Golden Bell Mound.”
Based on the burial goods and construction techniques, the tomb is believed to have been built between the end of the 6th century and the beginning of the 7th century, during the final phase of construction of keyhole-shaped tombs in Japan.
The identity of the person buried here is not known with certainty, but the individual is thought to have been a powerful leader of the lower Obitsu River basin, possibly the Makuta no Kuni no Miyatsuko, a regional ruler under the ancient Japanese political system.
The archaeological importance of Kinreizuka Kofun and its artifacts has been highly recognized. In 1959, the golden bells, stone coffin, and other excavated objects were designated as Important Cultural Properties of Japan.
The mound itself was designated a Chiba Prefectural Historic Site in 1950.
Kinreizuka Kofun was built on an alluvial plain formed by the Obitsu River, at an elevation of approximately 5.5 meters above sea level.
The plain contains a number of slightly elevated areas that were once sand dunes. Kinreizuka Kofun was constructed on one of these natural rises, taking advantage of terrain that stood somewhat higher than the surrounding land.
Historical records indicate that part of the mound was converted to agricultural land during the Meiji period. Later, urban development caused further loss of the original structure.
By the time of the 1950 excavation, the front portion of the keyhole-shaped mound had almost completely disappeared, leaving a form that resembled a circular burial mound.
Today, only part of the rear circular section remains, with residential areas surrounding the site.
The Gion-Nagasuka Kofun Tumulus Group consists of burial mounds constructed from approximately the early 5th century to the middle of the 7th century.
Kinreizuka Kofun is regarded as the last keyhole-shaped tomb constructed within the group. Its impressive scale and exceptionally rich burial goods suggest that the person buried there held a leading position among the regional elites of the time.
Maruyama Kofun, located nearby, was constructed around the same general period.
After Kinreizuka Kofun, the style of burial mound changed. One example is Matsumo Kofun, a square burial mound. This transition reflects the broader transformation of burial customs in Japan as the Kofun period drew to an end.
The original mound is estimated to have been approximately 100 meters long and constructed in two levels.
It was surrounded by two concentric moats, giving the entire complex an estimated length of approximately 140 meters when the moats are included.
The original mound is thought to have stood approximately 6 meters high. The surviving portion is now about 3.5 meters high.
The rear circular section contained a horizontal stone burial chamber with its entrance facing south. It is a type without projecting side chambers, known in Japanese archaeological terminology as a sode-nashi-gata stone chamber.
Partially cut stones were used in its construction, with particular attention given to the carefully laid cut stones forming the floor of the chamber.
This construction technique was relatively advanced for its time and demonstrates the sophisticated technology employed in the construction of Kinreizuka Kofun.
The burial chamber contained an exceptionally rich collection of objects. These included 21 decorated swords, golden bells, personal ornaments, gilt-bronze horse fittings, armor, mirrors, and other valuable artifacts.
The quantity and quality of these burial goods are remarkable even in comparison with other Kofun-period tombs in Japan. They provide important evidence of the wealth, authority, craftsmanship, and cultural connections of the person buried there.
Researchers also found Sue ware pottery and other artifacts associated with the burial. The absence of certain types of haniwa and other characteristics of the tomb support the estimated construction date of the late 6th to early 7th century.
Multiple individuals were buried within the stone chamber. The person buried inside the stone coffin is believed to have been a young adult male.
The exceptional collection of burial goods suggests that he belonged to the highest levels of the local elite and was likely a powerful regional leader.
Kinreizuka Kofun is an important archaeological site for understanding the final stage of keyhole-shaped burial mound construction in Japan.
Its size, sophisticated stone chamber, construction techniques, and extraordinary collection of burial goods provide valuable information about the technological development, political structure, and cultural environment of the late Kofun period.
The artifacts also offer clues about the status of local rulers and their connections with wider political and cultural networks in ancient Japan.
Kinreizuka Kofun is an important site for learning about the ancient history of the Kisarazu area. Although much of the original mound was lost through agricultural use and urban development, the surviving remains and excavated artifacts continue to provide valuable historical evidence.
Ongoing preservation, research, and public information efforts help convey the archaeological importance of Kinreizuka Kofun and the history of the powerful local leaders who lived in the Kisarazu region more than 1,400 years ago.