Burial Mounds Reveal 400 Years of Early Japanese History

Located east of Mount Nijo, the Kudo Kofun cluster is a designated National Historic Site in Kamimaki Town, Nara Prefecture. Kofun tombs are large burial mounds, often keyhole-shaped, built for Japan's rulers and elites from roughly the 3rd to 7th centuries.

In November 2025, it unexpectedly drew public attention after construction work to turn the area into a historic park damaged part of a stone burial chamber from a previously unknown tomb. The damage occurred because the excavation went ahead without the town first obtaining approval from the Agency for Cultural Affairs to change its construction methods.

The incident dealt a blow to local hopes of turning "the town's only nationally designated historic site into a place of rest and recreation." Yet it also brought renewed attention to the archaeological significance of this modest cluster of ancient burial mounds (tumuli).

Nestled amid residential housing, the site contains burial mounds constructed continuously over roughly four centuries, from the emergence of the Yamato polity (mid-third century) to the Asuka period (seventh century).

Burial Mounds Among Homes

*The hill at the center of the cluster, surrounded by housing developments. Burial mounds were constructed here continuously for 400 years (Provided by the Kamimaki Town Board of Education)*

The area around Kamimaki is mentioned in texts such as the Nihon Shoki, an early 8th-century court history that records Japan's founding myths and the reigns of its early emperors. It describes Kamimaki as an "upper pasture," and its gently rolling hills are said to have been suitable for grazing livestock.

At the tip of this ridge lies the Kudo Kofun cluster. Within an area measuring 170 meters (around 560 ft) north–south and 130 meters east–west, a total of nine burial mounds have been identified, including one newly discovered during the recent excavation. With the exception of Kofun No 1, a keyhole-shaped mound, the others are small, round or square mounds measuring under 20 meters. Even No 1, at 60 meters in length, is not particularly large.

At first glance, the group does not appear especially remarkable compared with other sites. Yet there was a clear reason it was designated a national historic site.

Saved By Excavation

Burial mounds from the 3rd century, the earliest phase of the Kofun period (about 300 to 358), through to the Asuka period, were all constructed at the same site, making the area unusually valuable from a historical perspective. An official from the town's Board of Education said that this long continuity is "critically important for understanding the political background of the Yamato polity."

The site first attracted wider attention in 2011, when plans surfaced to redevelop the area as a residential suburb of Osaka. Subsequent archaeological surveys conducted by the town and other institutions confirmed the presence of multiple tombs, leading to the development plan's cancellation. The area was subsequently designated a preservation district, paving the way for full-scale excavation.

A Princess Himiko-era Burial Mound

Analysis of excavated pottery identified Kofun No 3 as one of the oldest burial mounds in the cluster, dating to the 3rd century. The tumulus is square in shape, measuring 15 meters on each side. During excavation, soil disturbed from the site yielded a Chinese-made decorated bronze mirror with divine beasts known as gamontai-shinjukyo.

The mirror bears 48 characters, including the inscription gosakumeikyo (吾作明竟), an auspicious formula expressing wishes for prosperity across generations, along with relief images of immortals. Its design is identical to that of a mirror excavated from the Izumi Koganezuka Kofun in Izumi City, Osaka Prefecture, dated to the late 4th century.

The Izumi Koganezuka Kofun is also known for yielding another decorated bronze mirror bearing the inscription "the third year of Jingchu (239)." That date corresponds to the year in which Queen Himiko, the shaman-ruler of the early Japanese polity known as Yamatai, is recorded in Chinese sources as having sent tribute to the Wei dynasty in China.

This association has drawn attention to the occupant of Kofun No 3 as a potentially significant figure within the early Yamato polity.

"Located at the western edge of the Nara Basin, this area served as an early gateway for advanced culture arriving from Kyushu via the Seto Inland Sea and Osaka Bay," an official explained. "That may account for the inclusion of a Chinese-made mirror among the grave goods."

An Unusually Large Burial Site

Just 100 meters south of Kofun No 3 stands Kofun No 2, a round burial mound measuring 16 meters in diameter. Excavation of its horizontal stone chamber uncovered amber beads and a silver-mounted sword, identifying the tomb as dating to the mid-7th century Asuka period.

The mound was constructed to face south, with much of its rear deliberately cut away in accordance with Chinese feng shui principles. This method of construction is shared with imperial-class tombs, including the Takamatsuzuka Kofun in Asuka Village, renowned for its wall paintings depicting court life in the Asuka period.

A key clue to identifying the occupant lies 1.4 kilometers to the east, at the Bakuya Kofun in Koryo Town. The site is believed to be the tomb of Prince Oshisaka no Hikohito no Oe, a sixth-century imperial prince and son of Emperor Bidatsu, who ruled Japan during the Asuka period.

Dating to the late sixth century and measuring 50 meters in diameter, the Bakuya Kofun helps anchor the wider historical setting. Documentary sources and wooden tablets indicate that this area was controlled by Emperor Bidatsu and his descendants, strengthening the view that the individual buried in Kofun No 2 was closely connected to the Bidatsu imperial line.

Close to Prince Naka no Oe?

Alongside Kofun No 2, the cluster also includes Kofun No 6, which dates to the same period, suggesting that the area functioned as an important Asuka-era hub.

Why, then, were significant burial mounds constructed in succession at a site located more than 10 kilometers from the capital at Asuka?

According to the town's Board of Education, geography provides the key. "This area formed a key transportation corridor linking Nara and Osaka across Mount Nijo," an official said, adding that because it was "land directly controlled by the imperial family," it "became a natural location for the construction of important tombs."

As Kofun No 2 dates to the mid-7th century, scholarly attention has increasingly focused on Prince Naka no Oe, a great-grandson of Emperor Bidatsu and later known as Emperor Tenji.

After the Isshi Incident of 645, a palace coup that eliminated rival clans and reshaped Japan's early court politics, construction of the Earlier Naniwa Palace in what is now Osaka accelerated. The palace served as a major political center, increasing travel and communication between Naniwa (Osaka) and Asuka, the seat of the imperial court.

Located along this route, the Kudo Kofun area gained new strategic importance during the mid-7th century, when Prince Naka no Oe led a series of state-building reforms. Those measures, later known as the Taika Reforms, aimed to strengthen imperial authority and reorganize land and governance across the country.

The newly discovered kofun uncovered during the recent excavation also dates to the Asuka period. This raises the possibility that these graves belonged to figures who supported Prince Naka no Oe. New evidence from the discovery has shed light on the turbulent era surrounding the Taika Reforms.

Making the Cluster Accessible

*A conceptual rendering of the completed Kudo Kofun Cluster Historic Park (Provided by the Kamimaki Town Board of Education)*

Kamimaki Town held a residents' briefing in November 2025 to address the damage caused during the development of the historic park.

"Our intention was to improve the site, but the result caused concern," said Norihito Nagai, superintendent of education, adding that the situation was "deeply regrettable."

The town acknowledged that the damage could have been avoided had it sought approval from the Agency for Cultural Affairs for the change in construction methods and ensured that staff were present during the work. With many municipalities operating under limited staffing, the incident highlights a challenge likely shared nationwide.

Under the current historic park plan, the town aims to install walking paths around the tumuli and a small guidance facility, with completion targeted for fiscal year 2030. In addition to presenting the dynamic history of the Kofun period, the project seeks to raise public awareness of the importance of cultural heritage preservation.

(Read the article in Japanese.)

Author: Mitsuaki Obata, The Sankei Shimbun