Ryukakuji Iwaya Tumulus (龍角寺岩屋古墳)

Ryukakuji Iwaya Tumulus is a square tumulus in Sakae-cho, Inba-gun, Chiba Prefecture. It is the 105th tumulus of the 115 Ryukakuji burial mounds.

Ryukakuji Iwaya Tumulus is located on the plateau about 30 meters above sea level on the northern shore of Inba-numa Marsh. It is thought that this tumulus was constructed around the end of the seventh century in the Final Tumulus period. Each side of it is 78 meters long, and the mound is constructed from the three-step terraced slope. It is 13.2 meters high and is surrounded by the moats of 3 meters breadth and the embankments. The size of this tumulus surpasses even those of Kasuga Mukaiyama Tumulus (the burial mound of Emperor Yomei) and Yamada Takatsuka Tumulus (the burial mound of Empress Suiko) which were huge square tumuli in the same period, and as a square tumulus of this period, it is the largest in scale in all over Japan.

On the southern side, there are two horizontal stone chambers side by side with an interval of 10 meters. The western stone chamber measures 4.23 meters in depth, 1.68 meters in width of the inner back wall, and 2.14 meters in height. The eastern stone chamber is a little bigger than the western one, but at present it has collapsed. The building stone is tuffaceus sandstone, which contains a lot of fossils of shells that are produced in this region. It is unknown who was buried there. In 1970, the mound and the horizontal stone chambers were surveyed.

History of Survey
In 1970, the stone chambers were measured and the topography of the mound was surveyed by Meiji University.

In 2007, the cleaning topography containing the 104th tumulus was surveyed by Sakae Town Board of Education.

Designation as Historic Site
On January 27, 1941, it was designated as a national historic site. The management organization is Ryukaku-ji Temple.

Ryukakuji Aza Ikeshita 1601 and the others, Sakae-cho, Inba-gun, Chiba Prefecture.

Ryukakuji is written as (龍角寺) in the address of Iwaya Kofun, but in the name of the burial mounds, a Chinese character (竜) is usually used instead of (龍). Besides, in the name of Ryukaku-ji Temple near this tumulus, a Chinese character (龍) is used.

On the top of the mound of this tumulus, a triangulation point is placed. N35°49' 16".0031 E140°16' 37".5192.

[Original Japanese]