Since last year, archaeologists have been pulling layers of dirt away from the burial mound that measures 350 feet across and up to 32 feet high.
The mound is known as ‘kofun’ after the Kofun period of Japanese history when they were built between 300 AD and 710 AD, Live Science reports.
‘So far, we have conducted aerial laser surveys (first survey) and excavation surveys (second to fifth surveys), and obtained important results in clarifying the structure of the burial mounds,’ archaeologists shared in a press release announcing the discovery.
The survey showed ‘ritual’ spaces confined within the mound, which led the team to a grave pit where a clay box housing the coffin sat.
‘The coffin is believed to have been placed in a deeply recessed portion of the bottom of the grave pit, and a thin layer of clay and sand was leveled about 30cm outside the position where the coffin lid would be placed,’ according to the archaeologists.
And inside the coffin were the giant sword and mirror.
The six-inch blade sword, known as dakō, was likely never used but only fashioned to be laid with the deceased in the mound.
Read more: Giant 7-foot-long ‘demon slaying’ sword is discovered in a 1,600-year-old tomb in Japan: Archeologists say weapon was laid by the dead to help them fight evil spirits in the afterlife (astral world)