Nishiyamazuka Kofun is an ancient burial mound located in Kayō-chō, Tenri City, Nara Prefecture. It is a key feature of the Kayō subcluster of the Yamato Kofun Group, an area known for its concentration of large burial mounds associated with Japan’s early rulers. The tumulus is shaped like a keyhole, with a circular rear section and a rectangular front section. Although it has not been designated as a National Historic Site or received other major cultural property status, it is of considerable historical and archaeological interest.
The tumulus is believed to have been constructed in the first half of the sixth century, during the latter part of the Kofun period (approximately the third to seventh centuries). One prominent theory identifies it as the actual burial place of Princess Tashiraka, consort of Emperor Keitai, traditionally regarded as Japan’s 26th emperor. This possibility makes Nishiyamazuka Kofun particularly important to researchers investigating the imperial lineage and political history of ancient Japan.
In 2024, cofunia, an accommodation facility created by renovating a traditional Japanese house on the tumulus grounds, opened to visitors. The project offers a distinctive way to experience the area’s heritage while staying close to an ancient archaeological site. It also represents a new effort to connect local tourism with the preservation and revitalization of the surrounding community.
Nishiyamazuka Kofun stands on sloping ground at the western edge of a settlement in Kayō-chō, on the eastern side of the Nara Basin. It is a large keyhole-shaped burial mound, but no comprehensive archaeological excavation has yet been conducted.
According to records preserved in the Yamabe District Gazetteer, artifacts were discovered when the land was cleared for cultivation in 1887. These records provide valuable clues about the site, although many details of its original construction and burial facilities remain unknown.
The rear, circular section of the mound was built in three tiers, while the front, rectangular section has two tiers. Traces of fukiishi (stones laid over the mound’s surface) and haniwa (clay cylinders and figures placed around burial mounds) have been identified. Evidence also suggests that a moat once surrounded the tumulus.
The moat’s remains survive in the form of four irrigation ponds. Traces of an outer embankment have also been identified, indicating that the site was once an extensive and carefully planned funerary complex.
The structure of the original burial chamber has not been established. However, accounts of the land-clearing work in the Meiji period report the discovery of a stone coffin, magatama (curved comma-shaped beads), kudatama (cylindrical beads), bells, pottery, and objects described as artificial stone artifacts.
Unfortunately, these finds are no longer available for examination, and their present whereabouts are unknown. As a result, researchers have limited physical evidence with which to determine the identity of the person buried here.
The mound measures approximately 114 meters in total length. Its principal dimensions are as follows:
Rear circular section: 65 meters in diameter and 13 meters high, constructed in three tiers.
Front rectangular section: 70 meters wide and 8 meters high, constructed in two tiers.
One unusual feature is that the tumulus faces north. This orientation is rare among the burial mounds of the Yamato Kofun Group. Nishiyamazuka Kofun and Ninoséike Kofun are regarded as the only examples in the group with this north-facing arrangement.
The identity of the person buried at Nishiyamazuka Kofun remains uncertain. However, a significant theory proposes that it is the true tomb of Princess Tashiraka, the consort of Emperor Keitai.
Neither the Kojiki, Japan’s oldest surviving chronicle, nor the Nihon Shoki, an early official history, explicitly identifies her burial place. The Engishiki, a tenth-century compilation of regulations and court procedures, does list a tomb called Fusuma no Haka in its section on imperial mausoleums. Some researchers believe this reference may be connected to Princess Tashiraka’s burial.
In 1876, the Ministry of Religious Affairs designated Nishitonozuka Kofun in Nakayama-chō, Tenri City, as Princess Tashiraka’s tomb. The Imperial Household Agency continues to recognize it as her mausoleum.
However, archaeological estimates place the construction of Nishitonozuka Kofun in approximately the latter half of the third century, several centuries earlier than Princess Tashiraka’s presumed lifetime in the sixth century. This chronological discrepancy has prompted scholars to reconsider whether the officially designated mound is the correct burial site.
The theory that Nishiyamazuka Kofun is Princess Tashiraka’s actual tomb has been proposed as one possible explanation for this discrepancy. Two important points support the argument.
A rare large sixth-century mound: Nishiyamazuka Kofun is an unusually large keyhole-shaped burial mound dating to the sixth century within the Yamato Kofun Group, where many prominent mounds belong to earlier periods.
Connections through haniwa production: The haniwa associated with Nishiyamazuka Kofun are reported to have been made at the Niike Haniwa Kiln site, the same production center associated with haniwa from Imashirozuka Kofun in Takatsuki City, Osaka Prefecture. Imashirozuka Kofun is widely considered to be the burial place of Emperor Keitai.
These similarities have strengthened interest in the possibility that Nishiyamazuka Kofun was built for a member of the imperial family closely connected to Emperor Keitai. Nevertheless, the identification remains a theory rather than an established fact.
According to traditional accounts, Emperor Keitai became Japan’s 26th emperor after Emperor Buretsu, the 25th emperor, died without an heir. Keitai, known before his accession as Ōdo no Ōkimi, was said to be a fifth-generation descendant of Emperor Ōjin and was summoned from the region of Echizen, in what is now part of central Japan.
More than ten years passed between his accession and the establishment of his court in Yamato, the historical heartland of the early Japanese state. Some historians interpret this delay as evidence of political tensions between the new ruler and established power groups in the Yamato region.
In this political context, Emperor Keitai’s marriage to Princess Tashiraka, who belonged to the established imperial lineage, may have helped reinforce his legitimacy. The marriage is sometimes interpreted as a strategic union that connected the new ruler with the previous royal family.
If Nishiyamazuka Kofun was indeed Princess Tashiraka’s tomb, its location would also be significant. The mound lies in a region associated with major burial sites of the ancient Yamato rulers, near the Makimuku and Yanagimoto groups of tumuli. The choice of burial place may have carried political and symbolic meaning, reinforcing the connection between the imperial family and the traditional center of power.
Nishiyamazuka Kofun is a valuable archaeological site believed to date to the first half of the sixth century. Its impressive scale, unusual north-facing orientation, surviving traces of its moat, and reported connections with haniwa production all contribute to its importance in the study of Japan’s Kofun period.
The possibility that it is the true tomb of Princess Tashiraka adds another layer of historical significance, linking the site to questions about imperial succession and political alliances in ancient Japan. Although the identity of its occupant has not been confirmed, future research may help clarify its role in the history of the Yamato rulers.
With the opening of cofunia in 2024, Nishiyamazuka Kofun is also gaining a new connection to contemporary tourism. The combination of archaeological heritage and renovated traditional architecture offers visitors an opportunity to experience the historic landscape of Tenri in a distinctive way.