Shiroishi Inariyama Kofun

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Shiroishi Inariyama Kofun is an ancient burial mound from Japan’s Kofun period. It sits in the Shiroishi area of Fujioka, Gunma Prefecture, in the Kantō region of Japan. The mound is shaped like a keyhole when viewed from above (zenpō-kōen-fun) and is about 155 meters long. It was built in the early 5th century and is part of the Shiroishi kofun cluster. In 1993 it was designated as a National Historic Site of Japan, and in 2009 the designation was expanded to include two nearby kofun: Junitenzuka Kofun and Junitenkitazuka Kofun.

Location and structure
The mound sits on hilly ground about 1.5 kilometers south of the Aburagawa and Ayugawa rivers, at an elevation of roughly 120 meters. The rear circular part is about 92 meters in diameter and 13.5 meters high; the front rectangular part is about 81 meters wide and 8.5 meters high. The mound was originally covered with stones (fukiishi) and surrounded by clay figures (haniwa), including house-shaped ones. It is not clear whether there was a moat.

History and excavations
The kofun was first studied in 1933. In that work, two burial chambers were found in the rear circle, and many grave goods were recovered, such as bronze mirrors, magatama beads, iron weapons, and two unique stone pillows. Some of these items are now kept at the Tokyo National Museum. A ground-penetrating radar survey conducted from 2018 to 2019 revealed that the tomb is 155 meters long (not 140 meters) and suggested a third burial chamber inside the front part of the mound. The survey also helped date the mound to the early 5th century.

Nearby kofun
- Junitenzuka Kofun: about 36.8 meters long; circular part about 26.8 meters in diameter and 2.6 meters high.
- Junitenkitazuka Kofun: about 23 meters long; circular part about 22 meters in diameter and 2.2 meters high.

Access
The site is about a 20-minute drive from Gunma-Fujioka Station on the JR Hachikō Line.