The keyhole-shaped tomb is one of ancient Japan's most distinctive architectural forms. The Akatsuchiyama Kofun sits in the southeastern part of the Nara Basin, on an east-west ridge called Tōdaijiyama, surrounded by a cluster of burial mounds known as the Tōdaijiyama Kofun Group -- five keyhole-shaped tombs and forty to fifty smaller circular and square tombs dating from the early to middle Kofun period. Akatsuchiyama's remaining mound length measures 103.5 meters, with an estimated original length of 110 meters. The entire exterior was once covered in fukiishi -- a layer of cobblestones placed deliberately over the surface of the mound, giving it a finished, almost armored appearance. The posterior circular portion measures approximately 44 by 33 meters, with rounded corners and a projection at the tip that gives it a unique shape even among its keyhole-shaped peers.

The grave goods tell the story. Excavations of the sedimentary soil on the south side of the rear mound -- where a landslide destroyed the original burial chamber -- revealed fragments of a clay coffin, traces of vermilion pigment, stone bracelets, and stone replicas of ritual objects. But the most striking discoveries were the haniwa. These hollow clay figures, placed in rows around the perimeter of the mound, served as guardians and markers of sacred space. At Akatsuchiyama, the haniwa are predominantly cylindrical forms arranged in lines, but the collection also includes figurative pieces shaped like houses, lids, and chickens. During excavation, some rows of cylindrical haniwa were found still standing in place -- an extraordinary survival across more than a millennium and a half. The mound also yielded Haji ware pottery, linking the tomb to the domestic material culture of its era.

Based on the excavated remains and the tomb's position within the Tōdaijiyama group, archaeologists believe the Akatsuchiyama Kofun was built for a member of the Wani clan, one of the powerful families that dominated the Yamato heartland during the early Kofun period. The Wani were influential figures in the politics and culture of ancient Japan, and their cluster of tombs in the Tenri area speaks to generations of accumulated power and territorial control. The south side of the mound collapsed in a landslide at some point in history, and the front end was leveled, but enough remained to earn designation as a National Historic Site of Japan in 1992. The site was developed into a public park in 2009, accessible by a twenty-minute walk from Ichinomoto Station on the JR West Sakurai Line, transforming an ancient power statement into a quiet green space where visitors can trace the outline of a keyhole that once announced a ruler's immortality.