From the outside, the Tomio Maruyama burial mound in the city of Nara is unimpressive — the fenced-off property dotted with tree stumps, weeds and pebbles, and surrounded by modern residential buildings, certainly doesn't look like a treasure trove full of items with astounding historical value.
Yet in late 2022, a giant iron sword and a bronze mirror were unearthed from the tomb grounds, which date back to the late fourth century. The news stunned the nation, including even the most experienced archaeologists.
The 2.3-meterlong dakо̄ken sword — called that due to its wavy snake-like shape — is by far the longest sword found in East Asia from the Kofun Period (310 to 700), and possibly the world. It is also the oldest among the 90 or so dakо̄ken to have been discovered so far across Japan.
In another surprise, the bronze mirror — elaborately decorated with images of gods and animals — is shaped like a shield. Ancient mirrors are typically round; none with such a shape has ever been found.
“Archaeologists can make certain predictions about what types of items can be found in burial mounds, based on numerous past digs across the country and tens of thousands of excavation reports published about them,” said Shinya Fukunaga, an archeology professor at Osaka University who was not involved in the excavation of the Tomio Maruyama mound.
“But the items discovered there went far beyond our imagination. They were truly mind-blowing.”
The sword was unveiled to the public from late March through early April at an archaeological museum in the city of Kashihara, Nara Prefecture, attracting large crowds.
Experts say a series of surprise finds at the site could help untangle the many mysteries surrounding the rulers of fourth century Japan, often called the “blank” period, due to a lack of documentation in history books and restrictions on excavation work at imperial tumuli.
The historical find also shows how laser scanning and an emerging field of conservation science are playing an increasingly important role in archaeology.
Abandoned place
The Tomio Maruyama tumulus was a relatively obscure kofun, or ancient tomb, until the recent discovery of the sword and mirror, though its name had long been known among archaeologists. That’s because it was looted several times during the Meiji Era and its numerous treasures had been sold to collectors through antique dealers, many of which eventually ended up in museums, says Masaki Kanekata, who was head of the Nara Municipal Archaeological Research Center's excavation team that found the sword and mirror.
In 1972, during the area’s development as a residential district, experts from the Nara prefectural government conducted an archaeological dig of the site and confirmed the presence of a burial chamber at the top of the mound. While most of the items typically buried inside such chambers were gone, they unearthed small fragments of stone objects that had escaped the Meiji Era looting.
A land survey at the time also confirmed that Tomio Maruyama was a round tumulus with a diameter of 86 meters. The prefecture decided to protect it by designating the area as a public park while allowing businesses to go ahead and develop the surrounding areas.
“For about 50 years after that, the place was left abandoned,” Kanekata said. “It now looks like an island — a forest in the middle of a residential district. Because it was closed off with a fence, nobody could enter it, and even if they had tried to enter, they would have been stopped by the overgrown trees and weeds.”
Then in 2016, Nara city officials in search of a new tourism magnet set their sights on Tomio Maruyama. The city has a wealth of cultural assets on its eastern side, such as Todaiji Temple, home to the Great Buddha, and Kofukuji Temple, a symbol of Nara's past as an ancient Japanese capital, particularly with its five-story pagoda building.
In order to draw in tourists and revitalize the lesser-known western side of the city, the city government decided to fashion Tomio Maruyama into a proper historical site, according to Kanekata.
“So we decided to survey the area again in 2017, and this time flew a helicopter to scan the forest with lasers,” he recalled. “That way, we could conduct a detailed survey, without having to cut down any trees or grass.”
The aerial, three-dimensional laser scan revealed that the diameter of the tomb was in fact around 110 meters, larger than the original estimate of 86 meters — and any other round tumuli in Japan. A previously unknown tsukuridashi, a protruding stage-like square, was also found to have formed part of the tumulus.
This caused a media sensation, with major Japanese newspapers reporting the discovery on their front pages.
Measured expectations
A series of digs that began in 2018 focused on the tsukuridashi, which confirmed the existence of a second burial chamber toward the outer edge of the circle. It meant another person, in addition to the one at the top of the mound, was buried there.
Still, Kanekata recalled that his expectations for the site, which featured three circle terraces, were somewhat measured.
“Normally, a bottom chamber is considered subordinate to the top one,” he said. “So I didn't expect to find anything great.”
As the team of excavators kept digging, however, they stumbled across what looked like an iron bar. The team carefully removed the clay that enveloped the "bar" but could not find its tip until they dug beyond 2 meters.
“We had never seen anything like this, and a debate erupted on whether it was indeed one bar, or two or three bars that looked like one because they had rusted (over the years),” Kanekata said.
The team took the clay-covered discovery to the Archaeological Institute of Kashihara and ran an X-ray, which revealed that it was one large sword.
Many archaeologists couldn't believe it; they had never seen or heard about an ancient sword of this size before in Japan, or even in China or Korea, which had great influence on Japanese rulers at the time, he recalled.
Conservation science
Masayoshi Okuyama, a conservation specialist at the institute, said that work to confirm the sword’s structure was filled with tension, as the simple act of moving it for detailed analysis risked damaging it. In January 2023, when the institute’s staff carefully carried the sword into the building, they could barely fit it into the elevator and X-ray room.
After the X-ray images confirmed it was one whole sword, the painstaking work of cleaning it began.
Okuyama spent months working with surgical precision, examining the sword through a medical microscope and removing the minuscule pieces of clay “grain by grain” using a sewing needle taped to a wooden chopstick. His “laboratory excavation” work revealed the sword’s wooden handle and scabbard, parts of which were painted with black lacquer.
For Okuyama, conservation does not just involve cleaning and restoring historical artifacts as close to their original physical conditions as possible, but also preserving them along with their chemical properties.
“Cultural properties cannot be destroyed for analytical work,” said Okuyama, who has a Ph.D. in polymer chemistry for research on residue textiles often attached to the surface of excavated artifacts.
“Nondestructive and noncontact analysis is the first principle of conservation science.”
Minister-class fixer?
The discovery has raised questions among archeologists. The sword, at more than 2 meters, is too long to be used as a weapon, so why was it made? And why is the mirror shaped like a shield? Perhaps most importantly, who are the two people interred at the site?
The fact that the sword and mirror were buried at least makes it clear that the interred must have commanded huge political and military power. But the tumulus is round, and not keyhole-shaped, which suggests they did not belong to the imperial family, experts say.
Fukunaga theorizes that the top chamber housed a “minister-level” member of the Yamato Kingship, a loose alliance of local clans formed in Nara from the third century onward. While the start and origin of the Japanese state and imperial rule remain disputed by academics to this day, the Yamato Kingship is widely believed to have gradually expanded its hegemony to become the ruling force in western Japan by the mid-fourth century, before the birth of the full-fledged centralized state through the Taika Reform of 645.
Tomio Maruyama’s unique location is also noteworthy, Fukunaga says. The burial mound lies between the Saki burial mound cluster in the northwestern part of Nara city, erected in the late fourth century onward, and the giant tumuli at Mozu and Furuichi in Osaka Prefecture, which is located further to the west beyond the mountain bordering Nara and Osaka.
Over 200 tumuli at Mozu and Furuichi, including several giant ones shaped like keyholes, are believed to have been built shortly after the Saki burial mound cluster, between the late fourth century and the late sixth century. The Mozu-Furuichi burial mound cluster was designated a UNESCO World Heritage site in 2019.
Tomio Maruyama is located at the halfway point between the Saki and Mozu-Furuichi burial mounds, showing how the kingship’s forces moved from the south of the Nara basin to the north, and to the plains of Osaka, Fukunaga explained.
“I think the owner of the Tomio Maruyama mound was a newly risen holder of power who played the role of a 'fixer' during this politically volatile transition phase.”
The second interred person must have had a very close relationship with this minister-class clan leader, perhaps serving as the head secretary, he theorized.
Of course, there are other theories, including one that argues the person interred in the bottom chamber could have been a woman in charge of ceremonial duties, for example a priestess.
The mirror and the sword, meanwhile, were probably buried alongside the interred people to ward off evil spirits, as such items were believed to have magical powers, he said.
Imperial tumuli off limits
Interestingly, the finds at Tomio Maruyama offer insight into the types and quality of treasures hidden under imperial burial mounds, which house the tombs of emperors and empresses.
At present, the Imperial Household Agency, which manages 124 imperial tumuli across the country (of which 31 are in Nara Prefecture), prohibits the public from accessing the tomb premises, even for academic purposes, on the grounds that their peace and dignity must be protected.
“Now that we know the top-class rulers of the Yamato Kingship used to possess high-grade objects, I think there's a high likelihood of imperial tumuli holding equally impressive pieces of metalwork,” Fukunaga said.
But what's buried beneath the imperial tumuli is unlikely to see the light of day anytime soon, at least "not in my lifetime,” he said.
In his view, that's not such a bad thing.
Discovering novel objects is one of the greatest joys in archaeology, but research into ancient Japan's social and political structures is possible even without such rare finds.
“These tumuli have survived for over 1,500 years,” he said. “We don’t have to hurry. We can leave the fun of discovering the yet-to-be-dug-out (cultural assets) to people living here — 500 or 1,000 years from now.”
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