Kengoshizuka Kofun is an ancient burial mound in Asuka Village, Takaichi District, Nara Prefecture. This remarkable archaeological site is closely connected with the history of Japan’s early imperial court. Designated a National Historic Site, it has also yielded artifacts recognized as Important Cultural Properties of Japan.
The tomb is particularly notable for its rare octagonal shape. Excavations conducted between 2009 and 2010 revealed important details about its original structure and construction. The name Kengoshizuka contains the word kengoshi, another Japanese name for the morning glory, which explains why the tomb was once also called Asagaozuka Kofun. It is also known as Gozenzuka. Many researchers believe that it may be the tomb of Empress Saimei, who previously reigned as Empress Kōgyoku, although this identification is not conclusively proven.
Kengoshizuka Kofun stands on the edge of a hill near the boundary between Asuka Village and Kashihara City, at an elevation of approximately 126.3 meters. Its elevated position takes advantage of the surrounding terrain and views across the landscape. The site is located about 500 meters east of Iwaya-yama Kofun, another important National Historic Site.
The location and carefully planned construction suggest that the tomb was designed to make a powerful statement. Its distinctive form and elaborate stonework set it apart from many other burial mounds in the Asuka region.
Archaeological investigations established that Kengoshizuka Kofun was built as an octagonal mound using a technique known as rammed-earth construction, in which layers of soil are compacted to create a stable structure. The mound consists of three tiers and originally stood approximately 4.5 meters high. The distance between opposite sides of the octagon is about 22 meters.
A carefully constructed stone-paved feature surrounds the mound, following its octagonal outline. Each side measures approximately 9 meters, and the paved area is about 1 meter wide. It was made by arranging three rows of cut stones with considerable precision. The paving changes direction at angles of approximately 135 degrees, creating a geometric arrangement of nested octagons that mirrors the mound’s overall design.
Gravel was spread beyond the stone paving. Including the surrounding area, the entire structure is estimated to have measured approximately 32 meters across. The combination of the three-tiered mound, geometric stonework, and gravel surface demonstrates the sophisticated planning behind the monument.
One of the most remarkable discoveries was the recovery of hundreds of carefully shaped blocks of white tuff. These stones were cut into triangular-prism-like forms and are thought to have been stacked in a pyramid-like arrangement along the slopes of the mound.
Researchers estimate that approximately 7,200 stone blocks may have been used in the original construction. Their uniform shapes and carefully arranged surfaces suggest a high level of technical skill and a strong sense of architectural design during the Asuka period.
Measurements reconstructed from the remains indicate that the first tier had sides approximately 12.2 meters long, while the second tier had sides around 7 meters long. The surviving evidence helps researchers understand how the different levels of the octagonal mound were arranged.
Inside the mound is a side-entrance stone burial chamber that opens to the south. It was carved from enormous blocks of tuff breccia, with one major stone estimated to weigh approximately 80 tonnes. The stone is believed to have been transported from Mount Nijo, about 15 kilometers away, making the construction project an impressive logistical achievement.
The interior measures approximately 5 meters wide, 3.5 meters deep, and 2.5 meters high. A dividing wall separates the chamber into eastern and western compartments, allowing for the burial of two individuals. Each side contains a burial space approximately 2 meters long, arranged symmetrically. The walls were coated with two layers of plaster, creating a carefully finished interior.
The burial chamber had both an inner door and an outer blocking stone. The inner door, made of tuff, stands approximately 1.12 meters high, while the outer door, made of andesite, reaches about 2.4 meters in height. The scale and weight of these stones illustrate the engineering capabilities available to the people who built the tomb.
Small holes at the four corners of the inner door were designed to accommodate decorative metal fittings. These details suggest that the entrance was not merely functional but also carefully finished to reflect the importance of the burial ceremony.
The total weight of the stone materials used throughout the tomb is estimated to exceed 550 tonnes. Several hundred workers may have participated in the construction, while moving the heaviest stones by dragging them across the ground could potentially have required as many as 1,400 people. These estimates highlight the substantial labor and organization needed to create such an elaborate monument.
Excavations have uncovered fragments of a kyōcho-kan, a high-status coffin made by layering cloth with lacquer, along with numerous fittings and other burial objects. These include gilt-bronze coffin ornaments with geometric and floral designs, iron nails, metal clamps, glass beads, and human remains, including a molar tooth.
The kyōcho-kan was an exceptionally prestigious type of coffin in ancient Japan. Its construction required considerable craftsmanship, and its presence suggests that the tomb was intended for individuals of very high status. The decorative metal fittings also provide valuable information about the artistry and funerary customs of the period.
Many researchers believe that Kengoshizuka Kofun may be the burial place of Empress Saimei, one of the prominent female rulers of the Asuka period. She first reigned as Empress Kōgyoku and later returned to the throne under the name Empress Saimei. The tomb’s distinctive octagonal design and the exceptional quality of its construction have contributed to this identification.
Octagonal burial mounds are particularly associated with members of the imperial family during the 7th century, making the proposed connection historically plausible. Nevertheless, the identity of the person or persons buried here has not been definitively established, and the attribution to Empress Saimei remains a scholarly interpretation rather than a confirmed fact.
Improvements to the site were completed in February 2022, making the burial mound easier for visitors to explore. A designated viewing route and explanatory panels help introduce its unusual shape, construction techniques, and historical significance.
Reconstructed models of the burial chamber and replicas of excavated artifacts can be viewed at facilities such as the Asuka Village Buried Cultural Properties Exhibition Room. These displays help visitors imagine the original appearance of the tomb and appreciate the remarkable craftsmanship involved in its construction.
Asuka Village is one of Japan’s most important destinations for exploring the country’s early history. Its landscape contains numerous ancient tombs, temples, and archaeological remains that illuminate the development of the imperial court and the introduction of Buddhism.
Nearby attractions include Ishibutai Kofun, famous for its enormous exposed stone burial chamber, and Takamatsuzuka Kofun, renowned for its brilliantly colored wall paintings. Combining these sites in a day of sightseeing offers a broader understanding of the burial traditions, artistic achievements, and political culture of the Asuka period.
The area can be reached by public transportation from major railway hubs, including Kashiharajingū-mae Station. As access arrangements and local bus services may change, visitors should check current transport information and opening details before traveling.
Kengoshizuka Kofun is a fascinating monument that reveals the sophistication of ancient Japanese architecture. Its rare octagonal shape, thousands of precisely cut stone blocks, enormous burial chamber, and prestigious funerary artifacts all point to the power and resources of the elite who commissioned it.
Whether or not the tomb ultimately proves to be the resting place of Empress Saimei, it remains an outstanding archaeological site. For anyone interested in ancient Japanese history, imperial culture, and the remarkable engineering achievements of the Asuka period, Kengoshizuka Kofun offers a compelling glimpse into a world more than a thousand years old.