Kofun are megalithic tombs for rulers in Japan, constructed between the early 3rd century and early 7th century. The most common type of kofun has a shape of a keyhole, having one square end and one circular end, when looked down upon from above. The funeral chamber was located beneath the round part and consisted of a group of megaliths.
Daisen-kofun, the Emperor’s Nintoku tomb, in Sakai, Osaka. This is one of the largest tombs in the world (486 meters long). Today, three moats surround the tomb and the public is not welcome, but a walking path encircles the tomb if a curious visitor wants to look. (Image source)
Forty seven kofun, including the Daisen Kofun, make up the Mozu Tumulus. The other kofun were built not by emperors but by other wealthy elites of a growing Japan.
Like Egyptian Pharaohs, the Kofun aristocrats who were buried in the tombs were buried with bronze mirrors, swords, jewels, and other items. Today, the Imperial Household Agency has listed 740 kofun as tombs of imperial family members, although this number is in dispute. Neither the public nor archaeological teams are allowed into most of these kofun, although a team was permitted to enter the tomb of Empress Jingu in 2008.