In the heart of Osaka Prefecture lies one of Japan’s most awe-inspiring ancient monuments — the Daisen Kofun, a massive, keyhole-shaped burial mound believed to be the final resting place of Emperor Nintoku, who reigned during the 5th century. Spanning nearly 500 meters (1,640 feet) in length and surrounded by moats, it is the largest known burial mound in Japan and one of the largest in the world. For centuries, its mysteries have been protected by tradition, imperial authority, and the passage of time.
Yet a recent discovery has shed new light on what lies within this colossal tomb. For the first time in over a century, researchers have confirmed that certain artifacts — a knife and fragments of armor — once buried alongside Emperor Nintoku have resurfaced outside of the mound. Their journey from the tomb to the modern day tells a story of archaeology, secrecy, and historical intrigue.
The Daisen Kofun: Japan’s Monumental Tomb
The Daisen Kofun is part of the Mozu-Furuichi Kofun Group, a UNESCO World Heritage Site consisting of dozens of ancient burial mounds dating from the late 4th to the 6th centuries. These kofun were the burial sites of Japan’s most powerful rulers during the Kofun period (c. 250–538 CE), an era marked by political centralization and the emergence of the imperial court.
Shaped like a keyhole when viewed from above, the Daisen Kofun is surrounded by triple moats and covers an area of about 35 hectares (86 acres). Its sheer scale suggests the immense power and resources controlled by Emperor Nintoku’s court. Tradition holds that the tomb has never been opened in modern times — a reflection of the Imperial Household Agency’s strict policy of preserving imperial mausoleums as sacred sites.
The 1872 Landslide and Kashiwagi’s Investigation
While the Daisen Kofun is officially closed to excavation, history records at least one major breach into its secrets. In 1872, a landslide on the mound exposed part of the burial chamber. Japanese civil servant and scholar Kaichiro Kashiwagi led an investigation into the newly revealed interior.
According to historical accounts, Kashiwagi documented the chamber’s grave goods — swords, armor, jewelry, and other artifacts that testified to the wealth and status of the occupant. He reportedly sketched each item, recorded notes, and then ordered the objects reburied to maintain the sanctity of the tomb.
But rumors persisted that not all of the artifacts were returned.
A Discovery More Than a Century Later
In 2023, Kokugakuin University in Tokyo announced that it had acquired two remarkable objects from an art dealer: an ancient iron knife and fragments of lamellar armor. Wrapped with them was a piece of paper bearing Kaichiro Kashiwagi’s personal seal and handwritten notes linking the artifacts to the Daisen Kofun.
The provenance was further supported by their association with the personal collection of Takashi Masuda, a prominent art patron and businessman of the Meiji period who was known to have ties to Kashiwagi. Masuda’s collection had remained largely in private hands for decades, making these artifacts virtually unknown to scholars.
Scientific Confirmation
Following the acquisition, a team of archaeologists and materials scientists analyzed the knife and armor. They confirmed that:
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The metal composition and forging techniques matched those used in the 5th century Kofun period.
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The armor fragments were part of lamellar cuirass construction, common among elite warriors of the era.
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The corrosion patterns and soil residues matched samples from the Daisen Kofun’s surrounding environment.
With these findings, researchers could confidently assert that the items had indeed originated from Emperor Nintoku’s burial mound.
Historical Significance
The rediscovery of these artifacts is significant for several reasons:
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Rare Glimpse into a Sealed Tomb – Because the Imperial Household Agency restricts excavations, these items provide one of the few confirmed examples of grave goods from an imperial kofun.
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Material Evidence of Elite Status – The craftsmanship of the knife and armor speaks to the technological sophistication and military culture of Japan’s 5th-century elite.
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Validation of Historical Accounts – The objects corroborate Kashiwagi’s 1872 sketches and notes, providing physical proof of his investigation.
Ethical and Cultural Considerations
While historians and archaeologists are excited by the find, the case also raises sensitive questions about the treatment of imperial burial sites and the artifacts they contain. The Imperial Household Agency has historically maintained that imperial tombs are sacred, not archaeological, sites. Critics argue that this policy limits opportunities for research into Japan’s early history.
The fact that these artifacts left the tomb — whether through negligence, opportunism, or deliberate preservation — highlights the tension between cultural heritage protection and scholarly inquiry.
Connecting the Daisen Kofun to Japan’s Early State Formation
Artifacts like the knife and armor help contextualize the Daisen Kofun within broader regional and historical developments:
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Military Power – The presence of armor in the tomb aligns with historical interpretations of the Kofun period as an era when military prowess was integral to political authority.
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Continental Influences – The style of the knife and armor shows similarities to designs from the Korean Peninsula and China, reflecting the international trade and cultural exchange of the time.
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Ceremonial Importance – Such items were likely symbolic as well as practical, emphasizing the emperor’s role as both warrior and ruler.
The Ongoing Mystery of the Daisen Kofun
Despite this breakthrough, the Daisen Kofun still holds far more secrets than answers. Questions remain about:
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The full extent of the grave goods buried with Emperor Nintoku.
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The construction methods used for such a massive mound.
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The political and ceremonial functions of the surrounding moats and satellite tombs.
Unless the Imperial Household Agency changes its policy, these questions may remain unanswered for generations.
A Rare Bridge Between Past and Present
The reappearance of these two artifacts offers a tangible connection between modern Japan and its ancient imperial past. They are not merely objects — they are echoes from a time when emperors commanded armies, oversaw vast territories, and were buried in monuments designed to endure for millennia.
In this sense, the knife and armor fragments are more than archaeological curiosities. They are reminders of Japan’s early statehood, its technological and artistic achievements, and the enduring mystique of the Imperial line.
Conclusion: History Unearthed, if Only Briefly
The Daisen Kofun stands as one of the world’s most impressive ancient structures — and one of its most enigmatic. The confirmation that the knife and armor came from Emperor Nintoku’s tomb is a rare and invaluable insight into an otherwise sealed chapter of history. It is a story that blends 19th-century curiosity, 20th-century secrecy, and 21st-century science.
For now, the artifacts rest in the care of Kokugakuin University, where they can be studied and appreciated by scholars and the public alike. And while the tomb itself remains closed, these objects provide a fleeting but powerful glimpse into the life and death of one of Japan’s earliest emperors.