The burial chamber's construction sets it apart from nearly every other kofun in Japan. Rather than stacking slabs of stone to form walls and a ceiling -- the standard technique for Kofun-period tombs -- the builders of Ishinohoden selected two massive granite monoliths and hollowed them out to create a single enclosed room. The base stone measures 2.7 meters by 1.6 meters; the ceiling stone is larger, at 3.2 meters by 3.3 meters. Inside, the chamber is just 0.9 meters wide, 0.8 meters high, and 2.2 meters deep, with a narrow entrance only half a meter across. Round depressions on either side of the entrance suggest that a stone door once pivoted into place, sealing the dead within their granite shell. Two additional megaliths arranged outside form an entry portico facing south, giving the structure a formal, almost architectural quality that belies its compact size.

Behind the burial chamber, three megaliths stand in a row, and an archaeological survey conducted in 1988 confirmed that more stones continue underground to the west. The angle formed by these stones is 135 degrees -- a suggestive measurement. If the stones trace the outer perimeter of the original mound, the tumulus may have been octagonal, a shape associated with the highest ranks of Kofun-period society. Octagonal kofun are exceedingly rare, linked to imperial or near-imperial burials at the end of the period, when the old keyhole-shaped mounds were giving way to new geometric forms. A small fragment of Sue ware pottery found at the site helps date the tomb to the mid-seventh century, consistent with the octagonal theory. No full excavation has ever been conducted, however, leaving the question open and the stones keeping their counsel.

The burial chamber has been open to the elements for centuries, so no documented grave goods survive from the tomb itself. But Edo-period records tell a tantalizing story: at some point, a gold-copper burial vessel containing white bones was reportedly excavated from near the tumulus. The vessel's whereabouts are unknown. The Edo-period references prove that the site attracted attention long before the modern era -- visitors and local scholars noted its unusual construction and recorded what they saw. Yet no modern archaeological excavation has followed up on those accounts. The kofun sits on the grounds of the Kora Jinja shrine, a Shinto sanctuary that has protected the stones in its own way, keeping them within sacred space even as the surrounding city of Neyagawa grew up around them.

At an elevation of 100 meters on a gentle slope below Mount Ikoma, the Ishinohoden Kofun occupies the boundary between Osaka's urban sprawl and the forested mountains that separate it from Nara. Mount Ikoma itself has been a spiritual landmark for centuries, home to temples and shrines that draw visitors from across the Kansai region. The kofun sits at the foot of that tradition, a much older monument to different beliefs about death and the afterlife. Today the site is a fifteen-minute walk from Neyagawakoen Station on the JR West Katamachi Line, an easy detour from the commuter trains that carry passengers between Osaka and the eastern suburbs. The granite monoliths have watched the landscape transform around them -- from forested hillside to Shinto shrine grounds to the edge of a modern commuter city -- and they show no signs of yielding yet.