Kofun Period Breakthrough Reopens 150-Year Mystery at Emperor Nintoku's Tomb

For more than a century and a half, one of Japan's most tantalizing archaeological "sightings" has lived in a kind of academic limbo. It involves a handful of burial items said to have been taken from Emperor Nintoku's Tomb. Part of a UNESCO World Heritage site, the grave is Japan's largest keyhole-shaped tomb (kofun). It is administered today as an imperial mausoleum.

The objects were recorded during a Meiji-era investigation in 1872, yet afterward they effectively vanished. Researchers had only a drawing and scattered notes to go on. It left a nagging question hanging over Kofun-period (300-538) studies. Were these grave goods truly unearthed from the mound, or were they a misunderstanding, an exaggeration, or even a fabrication?

Now, those doubts have narrowed dramatically. Materials long known only from an old sketch, most notably a gilded, metal-mounted knife and fragments of armor, have been confirmed as actual surviving artifacts. The findings were presented at a public lecture held at Kansai University's Tokyo Center, where researchers walked the audience through how the long-lost items were traced, verified, and analyzed.

Putting the Pieces Together

A knife and armor fragments may sound like modest finds. But the significance here is what their confirmed existence does to several significant areas of understanding:

First, it strengthens what we can responsibly say about what was inside an imperial tomb. Because Emperor Nintoku's Tomb is managed under the Imperial Household Agency's system, full-scale archaeological excavation of the mound's interior is not permitted under current practice. That makes reliable evidence about its contents extremely rare.

It also shifts Kofun-period research from relying on a single sketch to studying real, physical objects. A sketch can preserve shape, but it can't reveal materials, internal structure, manufacturing steps, repairs, or technological choices.

*A gilded, metal-mounted knife, identified as a burial item from Emperor Nintoku's Tomb.*

The Meiji-period Mystery

The origin point is a 1872 episode: a burial facility in the tomb's front section was reportedly exposed, and items were documented. Over time, the most visible "proof" of them became a carefully made drawing and notes by illustrator Kaichiro Kashiwagi, who participated in recording what was found.

One of the speakers, Sakai City Museum senior curator Yoshikazu Sogo, underscored just how fragile that documentation was. Kashiwagi, he explained, never had the luxury of looking straight down and drawing a clean plan. Instead, "he just peeked in from the side through a tight gap, then tried to picture the overhead view in his head — and drew that."

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No Immediate Celebration

In 2024, researchers received word that materials linked to the 1872 investigation might still exist. The reaction was not instant celebration, but suspicion.

Tokuda Seishi, a Kansai University visiting professor, put the professional instinct sharply. "Archaeologists always err heavily on the side of suspicion," he said. "They tend to trust only what they have excavated themselves or what comes with a solid excavation record. Just being told 'someone has an artifact' isn't enough."

Verification Without Damage

Because cultural artifacts cannot be cut open for curiosity's sake, the team leaned on non-destructive techniques, especially X-ray CT (to see internal structure) and X-ray fluorescence (to identify elemental composition). CT shows how the object is built on the inside, while X-ray fluorescence shows what it's made of.

Those tests revealed details of manufacturing that are hard to fake convincingly, as they involve hidden layers and internal joins that only show up under imaging.

Ayako Watanabe, head of the cultural property research unit at Nippon Steel Technology, urged caution about judging artifacts by eye alone. "Surface clues don't always tell you everything," she said.

In her presentation, one example stood out: the structure of the gilded, metal-mounted knife. Analysis suggested a layered construction, with a gold-plated outer surface, a copper plate about 0.5 millimeters thick beneath it, and an iron blade core at the center. She added that the core appears to have been encased in hinoki (Japanese cypress) boards.

The gilding suggests a sophisticated and risky process. Drawing on chemical indicators, Watanabe said the gold finish was likely produced with a mercury-amalgam technique, a method that can release harmful mercury vapor during heating. "It's dangerous work for the craftsmen," she said, "but people at the time were already using this kind of technology."

Armor Fragments and the Timeline Question

The confirmed materials also pull researchers back into a classic Kofun-period puzzle: dating. Sogo noted that "the prevailing view was that the armor and the helmet were made in the second half of the fifth century." However, citing recent work by Tatsuya Hashimoto of Kagoshima University, he said the evidence points to an earlier date, possibly the first half of the fifth century.

The early fifth century is often seen as a period when Yamato, the Japan-centered polity based in the Nara Basin, often treated as the nucleus of Japan's early court, was strengthening its influence across regions.

If elite armor technology and prestige goods appear earlier than assumed, the chronology shifts. Furthermore, if they can also be plausibly linked to a monumental project like Emperor Nintoku's Tomb, the implications widen. It could push back the timeline for when power was consolidated and how that authority was displayed.

What Comes Next

Researchers stress that the work is still ongoing. Watanabe said some key manufacturing questions are still open, especially the order of assembly. "We still don't know whether the silver fittings were attached when the copper plate was mounted to the hinoki, or after the gilding was applied," she said. The next step, she added, is reconstructive testing to "verify the order of the steps" by trying to replicate the process.

Watanabe cautioned that analysis doesn't "directly hand us ancient manufacturing techniques." But it does provide "the objective grounds needed to get closer to what was real," she concluded.

Author: Daniel Manning