History and Background
Musa Ōtsuka Kofun is believed to have been built in the late 6th century, during the final stages of the Kofun period. The mound measures approximately 30 meters in diameter and 8.5 meters in height. Although roads around the site have encroached on its base, reducing its original size, archaeological estimates suggest that the mound would originally have measured more than 40 meters in diameter and over 10 meters in height.
The tomb stands near the point where the Asahi River flows out onto the plains, close to an important crossing on the ancient San’yōdō highway. Given this strategic location, the person buried here is thought to have been a powerful regional leader, possibly a kuni no miyatsuko, a local ruler responsible for governing the area and controlling transportation routes. Another possibility is that the tomb belonged to a member of the Jōdō clan, a powerful family believed to descend from Kibitsuhiko-no-Mikoto.
The Impressive Stone Burial Chamber
On the southern side of Musa Ōtsuka Kofun, a horizontal stone burial chamber opens into the mound. Constructed from enormous granite blocks, it features a distinctive layout with side chambers branching from the central passage.
The entire chamber measures approximately 18 meters in length. The main burial chamber is 6 meters deep, 2.8 meters wide, and 3.2 meters high. Its entrance passage is approximately 12 meters long and widens toward the entrance, measuring between 1.8 and 2.4 meters across.
Inside the main chamber rests a house-shaped stone coffin made from shell-bearing limestone. It measures 2.88 meters long, 1.6 meters wide, and 1.5 meters high. The stone, known as Namigata Stone, was quarried in what is now Ibara City, Okayama Prefecture. The scale of the coffin and the massive stones surrounding it demonstrate the importance of the person buried here.
Cultural Heritage and National Designation
Musa Ōtsuka Kofun was designated a National Historic Site in 1930. This recognition reflects its considerable archaeological and cultural importance as one of Okayama Prefecture’s major ancient burial sites.
The tomb was constructed during a period when the Jōdō clan was believed to have been a powerful family in the ancient Kibi region. Although the identity of the person buried here remains uncertain, weapons, armor, ornaments, and other valuable grave goods may once have been placed inside the chamber, as was customary for high-ranking individuals of the period.
The Surrounding Area and Related Historic Sites
Musa Ōtsuka Kofun lies somewhat away from the principal territory of the ancient Kibi Jōdō clan, which was centered around the Takashima and Ryūsō school districts on the eastern bank of the lower Asahi River. Nevertheless, its proximity to the ancient San’yōdō highway made this area an important transportation hub, and it is thought that the Jōdō clan established a burial site here to demonstrate its regional authority.
Behind the burial mound rises Mount Takakurayama, which was known in ancient times as Kunimidake. The mountain is associated with agricultural and ritual practices, including ceremonies related to assessing the prospects for rice cultivation. At its foot stands Takakura Shrine, an important local place of worship.
The shrine’s stone plaque above the torii gate dates to 1332, the first year of the Shōkei era. It bears an inscription naming the chief donor as Jōdō Sadanari, a Shinto priest. This inscription provides evidence of the Jōdō clan’s close involvement in the region’s religious ceremonies and traditions.
Exploring the Ancient Kibi Region
Musa Ōtsuka Kofun is more than an impressive archaeological monument. It helps illuminate the political power, transportation networks, and religious traditions of ancient Kibi. Nearby sites include Takakura Shrine, whose inscribed stone plaque is designated a cultural property by Okayama City, and the Hayashibara Kofun burial mound cluster north of Asahi River Bridge.
Exploring these sites together offers a deeper understanding of the region’s history and the people who shaped it. For travelers interested in ancient Japan, Musa Ōtsuka Kofun is a rewarding destination where monumental stonework and the surrounding landscape bring the distant past to life.