What happened
Three moats ring it, and the mound holds something like 1.4 million cubic metres of earth; estimates of the labour run to more than a million man-days over fifteen years or more. Nobody may go in. The Imperial Household Agency administers it as a grave and has never permitted a full excavation, which is why the Nintoku attribution — made in the Edo period from a chronicle written centuries after the burial — cannot be tested against the mound’s own date. It was inscribed as UNESCO World Heritage in 2019 with the rest of the Mozu-Furuichi group.
By footprint it ranks among the largest tombs on earth, alongside Egypt’s great pyramids and the mausoleum of the First Qin Emperor.
Background
Building on this scale demanded enormous organized labor sustained over years — evidence of the power the Yamato polity could command.
Consequences
The mound has never been scientifically excavated; the Imperial Household Agency restricts entry, though limited joint surveys have begun in recent years. As part of the Mozu-Furuichi kofun group it became UNESCO World Heritage in 2019. It remains the most visible monument of the age when the Yamato kings consolidated Japan.