Hiranotsuka Anayama Kofun is an ancient burial mound located in Hirano, Kashiba City, Nara Prefecture. It is part of the Hirano Kofun Group and is an important archaeological site that sheds light on the burial customs and political culture of ancient Japan. Designated a National Historic Site in 1973, the mound is believed to have been built for a person of royal or otherwise high status. One theory associates it with Prince Chinu, although the identity of the person buried here remains uncertain.
The kofun stands on the southern slope of a low hill extending from Mount Myojin in western Nara Prefecture. It is a square burial mound built in two tiers. The lower tier measures approximately 25–30 meters on each side and stands about 2.7 meters high. The upper tier measures around 17.4 meters on each side and is also approximately 2.7 meters high, giving the mound a total height of about 5.4 meters.
The mound was constructed using a technique known as rammed-earth construction, in which layers of clay-rich and sandy soil were alternately laid down and compacted to create a firm structure. Its exterior was finished with facing stones made from tuff quarried from Mount Nijo, giving the mound a carefully constructed appearance.
One of the site’s most remarkable features is its stone burial chamber, which opens toward the south. It is an early example of a side-entrance stone coffin chamber, a type of burial facility that reflects the transition from traditional horizontal stone burial chambers to more specialized stone-coffin structures during the late Kofun period.
The chamber is made from tuff blocks from Mount Nijo and measures approximately 4.47 meters in total length. Its principal burial room is about 3.05 meters long, 1.50 meters wide, and 1.762 meters high. The entrance section measures approximately 0.562 meters long and 1.192 meters wide, while the passage leading to the entrance is around 0.820 meters long and 1.40 meters wide.
Burial containers found inside included a kyōcho-kan, a lacquered container made using layers of cloth and lacquer, as well as a lacquered basket-shaped coffin. Excavations also uncovered fragments of gold rings, hollow beads, and a copper bowl. These objects provide clues about the status and burial practices of the individual interred here.
The identity of the person buried at Hiranotsuka Anayama Kofun has not been established. However, the mound’s scale, elaborate construction, and distinctive burial chamber suggest that its occupant belonged to the upper ranks of ancient society.
One prominent theory identifies the occupant as Prince Chinu, also known as Chinu no Miko. He was a son of Emperor Bidatsu, traditionally regarded as Japan’s 30th emperor, and the father of Emperor Kōgyoku, who later reigned again as Empress Saimei, and Emperor Kōtoku. Despite these important family connections, historical records such as the Kojiki and Nihon Shoki provide little detailed information about his life. The proposed connection between Prince Chinu and this tomb therefore remains a theory rather than an established fact.
Hiranotsuka Anayama Kofun is thought to have been constructed during the latter half of the 7th century, possibly toward the end of that century. Its early form of side-entrance stone burial chamber makes it a valuable site for understanding changes in Japanese burial architecture during this period.
Researchers have also noted similarities between its burial structure and the tombs of the Neungsan-ri Ancient Tombs in present-day South Korea, associated with the royal family of the ancient Korean kingdom of Baekje. These parallels offer an important perspective on cultural connections between Japan and the kingdoms of the Korean Peninsula during ancient times.
The kofun was designated a National Historic Site in 1973, and the protected area was expanded in 2018. In 2020, the site was developed as Hiranotsuka Anayama Kofun Historic Site Park and opened to the public.
Visitors can appreciate the burial mound and its historical setting, but access inside the stone burial chamber is generally permitted only twice a year, during special openings in spring and autumn. Anyone hoping to see the interior should check the latest public-opening schedule in advance.
The Kashiba City Museum of Nijo Mountain is located nearby and offers further information about the region’s archaeology, including the ancient tombs and stone materials associated with Mount Nijo. It provides useful context for understanding the construction techniques and historical significance of the kofun.
The site can be reached on foot in approximately 20 minutes from Shizumi Station on the JR Kansai Main Line.
Hiranotsuka Anayama Kofun is a valuable historical site that reveals the sophistication of ancient Japanese burial practices and the social standing of the people who commissioned such elaborate tombs. Its carefully built mound, distinctive stone chamber, and possible connections to the royal family make it a fascinating destination for travelers interested in archaeology, early Japanese history, and the cultural exchanges that shaped East Asia.