National Treasures & Important Cultural Properties
of National Institutes for Cultural Heritage, Japan

The Tenjinyama Kofun is part of the Yanagimoto Kofun cluster located to the east of the Yamato Basin and is a 113-meter-long large keyhole-shaped tomb mound located to the west of the Sujin Emperor's grave. These copper mirrors were found inside and outside of a wooden box in a stone chamber located at the center of the circle part. The box contained 41 kg of cinnabar surrounded by 20 mirrors placed with the mirror side facing upward and three mirrors were also placed outside the box. Other items including an iron knife, an iron sword, iron arrowhead, a small knife and a hook were also found inside and outside of the box. The mirrors were placed clockwise along the wooden box from the north and twenty mirrors completed the circle. Outside of the box, two mirrors were placed in the north and one mirror was placed in the south. The details of the mirror types were as follows:
Houkakukiku mirror: 6
Nikoukamon mirror: 4
Gamontaishinjyu mirror: 4
Jyukei mirror: 4
Gazo mirror: 2
Sankakubuchihenkeishinjyu mirror: 2
Jinbutsuchojyumoumon mirror: 1

The age of the Tenjinyama Kofun is thought to date from the late fourth century. However, these mirrors found in the Kofun are an unusual combination of mirrors, which does not include any of the Sankakubuchishinjyu mirrors commonly found in Kofun of the early fourth century, but mainly includes Houkakuki mirrors and Naikoukamon mirrors from the Later Han Dynasty. Given that no buried human bodies were found in this Kofun, it may be a Kofun (called Baicho) where only relics from the Sujin Emperor's grave were buried.