Size and Distinctive Features
Nyotaisan Kofun was built on a plateau approximately 40 meters above sea level. The mound measures approximately 106 meters in total length.
The main circular section has a diameter of approximately 84 meters and is about 7 meters high. The projecting section measures approximately 18 meters wide and 16 meters long.
Its unusual shape resembles a scallop shell, which is why this type of burial mound is called a hotategai-gata kofun. In terms of size, Nyotaisan Kofun is considered one of the largest examples of this type in Japan, ranking approximately third nationally and among the largest in the Kanto region.
The surface of the mound was covered with fukiishi, or stone coverings, a feature commonly found on large Kofun-period burial mounds. Cylindrical haniwa figures are also believed to have been arranged around the mound.
These stones and clay figures helped distinguish the burial mound as a sacred space while also emphasizing the status and authority of the person buried within.
When Was It Built and Who Was Buried Here?
Based on the characteristics of the haniwa and other archaeological evidence, Nyotaisan Kofun is generally believed to have been constructed during the middle Kofun period, from the early to middle 5th century.
Because large-scale archaeological excavation of the mound has not been carried out, the exact nature of its burial chamber remains uncertain. However, researchers believe that it probably contained a pit-style burial facility typical of the period.
In addition to cylindrical haniwa, fragments of shield-shaped and other figurative haniwa have been found. Such objects provide valuable clues about burial rituals, social organization, and the beliefs of people living in ancient Japan.
The identity of the individual buried here is not known. However, given the tomb’s close proximity to the enormous Ota Tenjinyama Kofun, researchers have suggested that the person may have belonged to the family or close circle of a powerful clan that ruled the Kamitukeno region, corresponding broadly to present-day Gunma.
The Relationship with Ota Tenjinyama Kofun
One of the most fascinating aspects of Nyotaisan Kofun is its close relationship with the neighboring Ota Tenjinyama Kofun. The two tombs are located very close to each other, and their principal axes are oriented in almost the same direction.
Research has also revealed evidence that the tombs were designed using Shaku measurements associated with ancient East Asian measurement systems. A basic unit of approximately 25 shaku, or about 6 meters, appears to have been incorporated into their layout.
This carefully planned arrangement suggests that the two tombs may not have been built independently, but rather as part of a coordinated burial complex.
Research further suggests that Nyotaisan Kofun may have been constructed slightly earlier than Ota Tenjinyama Kofun. This has led to the possibility that the individuals buried in the two tombs were connected through family ties or close political relationships.
National Historic Site
Nyotaisan Kofun was designated a National Historic Site in 1927 in recognition of its historical and archaeological importance.
It is regarded as an important example of the scallop-shell-shaped burial mound tradition and contributes to our understanding of Kofun-period culture in the Kanto region and throughout Japan.
The mound and its surrounding area have been relatively well preserved, allowing visitors to appreciate the scale and form of an ancient burial monument. It remains an important part of Ota City’s cultural heritage and is carefully protected as a historic site.
A Fascinating Destination for History and Archaeology
Nyotaisan Kofun can be visited together with the neighboring Ota Tenjinyama Kofun, making it possible to explore the relationship between these two monumental tombs. The two sites are only a few minutes apart on foot, allowing visitors to imagine the impressive landscape created by the construction of powerful rulers’ tombs during the Kofun period.
The surrounding area is relatively green and peaceful, making it a pleasant place for a historical walk. As visitors explore the site, they can imagine how this landscape may have appeared more than 1,500 years ago.
For travelers interested in Japanese history and archaeology, Nyotaisan Kofun provides an opportunity to encounter the ancient burial culture of eastern Japan in an atmospheric setting.
Ota City is home to many other ancient burial mounds and archaeological sites, making the area particularly suitable for exploring Japan’s Kofun-period heritage. Nyotaisan Kofun is one of the key historic sites for understanding this rich archaeological landscape.
Access
Nyotaisan Kofun is located approximately 1.7 kilometers from Ota Station on the Tobu Railway network. The site can be reached on foot or by bicycle, and the nearby Ota Tenjinyama Kofun makes it convenient to combine the two sites as part of a historical walking route.
Walking between these ancient monuments while imagining the landscape of the Kofun period offers a unique way to experience the history and culture of the eastern Gunma region.