SAKAI, Osaka Prefecture--The Imperial Household Agency and Sakai city government began their first joint excavation project Oct. 23 on the nation's largest burial mound, apparently built for an emperor over 1,500 years ago.

The group in charge of the dig, seven people from the agency and city government, gathered at the keyhole-shaped Daisen “kofun” burial mound via an entrance on its north side around 8:25 a.m.

The site, also known as Nintoku-ryo kofun (Tomb of Emperor Nintoku), is about 486 meters long and 307 meters wide, and surrounded by a three-tiered moat.

Researchers plan to dig three trenches about 2 meters wide and 28 to 30 meters long across the embankment around the moat immediately surrounding the mound, one on the eastern side and two on the southern banks.

The excavation is scheduled to be completed in early December.

The team is planning to locate the original surface of the embankment where archeological artifacts, such as “haniwa” pottery objects, could be found and assess the conditions of the embankments.

The Imperial Household Agency is planning to conduct revetment work in coming years on the mound and embankments as part of conservation work for the entire site.

It hopes to gain basic data to help plan future revetment work from the project.

“We hope to achieve a positive outcome with cooperation from Sakai city,” Masashi Tokuda, an Imperial burial mounds researcher from the agency, told The Asahi Shimbun in an interview before excavation commenced.

The agency lists the burial mound as the tomb of Emperor Nintoku.

However, it has refused scholars permission to conduct extensive research on the mound, and the claim has never been archeologically proven.