What happened
In the 5th century (c.), Japan’s largest burial mound was built at Sakai in present-day Osaka: the keyhole-shaped Daisen Kofun, about 486 meters long and ringed by moats. The Imperial Household Agency designates it the mausoleum of Emperor Nintoku, an attribution scholars continue to debate.
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.