The Imperial Household Agency said Monday it will jointly excavate Japan's largest ancient mounded tomb with a local government for the first time.
The agency had restricted such a survey in Daisen Kofun, which was first built in the fifth century and is officially designated as the tomb of Emperor Nintoku, saying the mound is "the imperial family's tomb where peace and sanctity needed to be maintained."
The excavation survey starting later this month in one of the dikes surrounding the massive tomb in Sakai, Osaka Prefecture, will be part of the tomb's preservation efforts conducted with the municipal government and its results will be published at the end of November.
When it surveyed the same dike in 1973, the agency discovered clay figures made for ritual use.
Calls for the joint survey had been increasing among academics and others as the mound has been gradually eroded by water in the surrounding moats. The agency is expected to refer to results of the survey when it conducts reinforcement work.
The agency has judged it necessary to cooperate with local authorities which have long engaged in protecting the cultural asset, one of its officials said.
Japan is seeking to register an ancient tumulus cluster covering the Daisen tomb as a UNESCO World Cultural Heritage site.
The tomb is known as one of the three largest in the world, together with the Mausoleum of the First Qin Emperor in China and the Great Pyramid of Khufu in Egypt.