The Shibayama Kofun Group is a nationally designated historic site located in Nakadai, Yokoshibahikari Town, Sambu District, Chiba Prefecture. Although it is known as the “Shibayama Kofun Group,” the site is actually located in Yokoshibahikari Town, not neighboring Shibayama Town. It is also sometimes referred to as the Nakadai Kofun Group.
The site is particularly famous for the haniwa clay figures excavated from Tonozuka Kofun and Himezuka Kofun. These artifacts are designated as Important Cultural Properties of Japan and provide valuable information about burial customs and artistic expression in ancient Japan.
The Shibayama Kofun Group was constructed on a plateau along the eastern bank of the Kido River, which flows through the central part of the Kujukuri Plain.
The group centers on two large keyhole-shaped burial mounds, Tonozuka Kofun and Himezuka Kofun, with another 13 round burial mounds scattered around them.
In 1956, an archaeological excavation was conducted by Waseda University. The discovery of haniwa arranged in remarkably well-preserved formations was particularly significant and became an important archaeological discovery in Japan.
Tonozuka Kofun is a keyhole-shaped burial mound measuring approximately 88 meters in total length, with its square front section facing west.
The mound was constructed in two tiers. The rear circular section rises approximately 10 meters high, while the front section is approximately 10.4 meters high. A double rectangular moat system, accompanied by an outer embankment, surrounds the mound.
Numerous cylindrical haniwa have been discovered on the mound. Excavations also uncovered animal-shaped haniwa depicting horses, dogs, deer, and wild boars, as well as bird-shaped figures, objects representing ceremonial equipment, and human figures.
The burial chamber is a horizontal stone chamber. The interior was coated with red pigment, and burial goods including magatama beads, gold rings, and gilt-bronze ornaments were found inside.
Himezuka Kofun lies approximately 30 meters north of Tonozuka Kofun. It is another keyhole-shaped burial mound, measuring approximately 58.5 meters in total length.
The rear section is approximately 4.4 meters high, while the front section reaches about 5 meters. The fact that the front section is slightly higher than the rear section is one of the mound’s distinctive characteristics.
A horizontal stone chamber is located on the southern side of the mound. Excavations uncovered a gilt-bronze decorated sword, horse-riding equipment, and various beads and ornaments.
One of the most important discoveries at Himezuka Kofun was the line of haniwa surrounding the burial mound. Human and horse-shaped haniwa were found in positions believed to be close to their original locations.
Because the arrangement was preserved so well, the discovery has exceptionally high academic value. The figures are considered important evidence of the development of haniwa art during the late 6th century, when the production and artistic expression of these clay figures reached a particularly sophisticated stage.
Tonozuka and Himezuka Kofun are believed to have been constructed between the late 6th century and the beginning of the 7th century.
Based on archaeological research at these and nearby burial mounds, researchers believe that Tonozuka Kofun was constructed first, followed by Himezuka Kofun. This suggests that the cemetery developed over time as the local society changed.
The haniwa excavated from the Shibayama Kofun Group are designated as Important Cultural Properties of Japan and are preserved at Kannekyoji Temple. The figurative haniwa from Tonozuka and Himezuka are particularly valuable examples of ancient Japanese art.
These haniwa were first designated as Tangible Cultural Properties of Chiba Prefecture in 1971. In 2024, they were elevated to the status of nationally designated Important Cultural Properties.
The Shibayama Kofun Group was designated as a National Historic Site in 1958. The mounds and archaeological remains have been well preserved, allowing visitors to appreciate an important part of the region’s ancient history.
The area surrounding the Shibayama Kofun Group contains numerous other archaeological sites and burial mounds.
Upstream along the Kido River are the Yamada and Hoba Kofun Groups, while downstream are the Yamamuro Himezuka Kofun and Otsutsumi Gongen-zuka Kofun in neighboring Sambu City.
Visitors can also explore archaeological sites dating from much earlier periods, including the Nakadai Shell Midden and Konosu Shell Midden, which provide evidence of life during the Jomon period of prehistoric Japan.
The Shibayama Kofun Group is an important archaeological site where visitors can explore the history and culture of ancient Japan. The two major keyhole-shaped tombs, their stone burial chambers, and especially the remarkable haniwa discoveries offer a glimpse into the beliefs, burial customs, craftsmanship, and social structure of the Kofun period.
For travelers interested in Japanese archaeology and ancient history, the site provides a fascinating opportunity to learn about the people who lived in the Kujukuri region more than 1,400 years ago.