The Imperial Household Agency and the city of Sakai in Osaka Prefecture, western Japan, have begun a joint survey of the largest ancient burial mound in the country.
The keyhole-shaped mound in Sakai City is believed to be the resting place of fifth-century Emperor Nintoku.
It is the first study of the site conducted by the agency together with outside archeologists and researchers.
The agency controls ancient imperial burial sites and has long restricted entry to outsiders, citing the need to protect their serenity and dignity.
Local archeologists with in-depth knowledge of ancient tombs in the area are participating for the first time.
The burial mound is surrounded by 3 moats. On Tuesday, 10 project members checked the embankment built between the 2 inside moats.
They will dig in 3 locations to study the structure of the embankment and see if any clay figure artifacts can be found. The survey will continue until early December.
Agency researcher Masashi Tokuda says the team will cooperate with Sakai City and hope to produce good results.