Not all weapons are to be used against other humans. Sometimes, we need them to fight evil spirits — at least that’s what some people in Japan thought. Researchers have uncovered a 2.3 meters iron sword during diggings of a 1,600-year-old burial mound near the city of Tara, in the Saga prefecture. The sword was so large that it was likely only used as a means of protection for the deceased against evil spirits, the researchers say.

Riku Murase, an archaeologist for Nara City, led the team that found the sword and a bronze mirror while excavating a site called Tomio Maruyama back in November. The burial mound is located in a park west of Nara and dates from the fourth century AD. “It was so long I doubted it was true,” Murase told Live Science about the sword.

The weapon is also known as a Dako sword, with a distinctive undulating blade. Dako swords have been found in other Japanese tombs but the size of this one is exceptional — it’s the largest one ever discovered. The shield-shaped decorated mirror was also the first of its kind to be discovered. This allows both items to be classified as national treasures, experts said.

A remarkable finding

The Nara region is packed with thousands of burial mounds known as “kofun” after the Kofun period of Japan when they were built, between A.D. 300 and 710, Live Science said. Kofun can also be found in other places in Japan, with estimations of 160,000 across the country – the largest ones measuring up to 60 meters across.

“This indicates that the technology of the Kofun period are beyond what had been imagined, and they are masterpieces in metalwork from that period,” Kosaku Okabayashi, the deputy director for Nara Prefecture’s Archaeological Institute of Kashihara, told Japan Times. “They are masterpieces in metal work from that period.”

The Tomio Maruyama burial mound, where the sword and the shield were found, is one of the largest kofuns in Japan, with a diameter of 100 meters and a height of 10 meters. It is thought to have belonged to a powerful individual related to the imperial Yamato family. Previous excavations have found a large coffin and no human remains.

Mirrors and shields are considered to be tools to protect the dead from evil spirits. The sword is thought to have been enlarged to increase its power. Archaeologist Stefan Maeder, an expert in Japanese swords, not involved in the study, told Live Science there was a tradition in Japan of large swords being offered to powerful spirits.

The mirror is 64 centimeters long and 31 centimeters wide and weighs 5.7 kilograms. It features geometric designs and patterns seemingly based on imaginary characters, and it has tin, copper, and lead, based on an X-ray. Meanwhile, the sword has a snake-like shape and markings that represent a sheath and a handle.

If you happen to be in Japan, the excavation area is open to the public. However, the mirror and the sword won’t be exhibited as they are going through preservation work. For the researchers, the finding was just incredible. More research will likely follow to get a better understanding of the role of the sword and the mirror and the burial mound.