Discovery and Archaeological Excavations
Jusanpozuka Ruins attracted renewed attention in the 1970s, when plans were being made to develop an industrial park in the area. Archaeological excavations were conducted between 1973 and 1976, revealing a large group of remains dating from the Nara through Heian periods.
The surrounding area is one of the most archaeologically rich parts of Isesaki. Approximately 1.5 kilometers northeast of the ruins lies the Shimoya Kofun Group, a collection of ancient burial mounds.
To the north of the site once ran the Tosan-do Station Route, an important ancient highway connecting eastern regions of Japan. Its proximity to this major route suggests that Jusanpozuka was situated in an important location for transportation and regional administration.
Excavations uncovered not only the temple complex but also residential buildings, wells, workshops, and other structures. Because some of the buildings were laid out in a highly organized manner, the site was initially thought by some researchers to have been the remains of the administrative headquarters of Sawi District.
However, the large number of Buddhist artifacts discovered at the site, including fragments of Buddhist statues and ritual objects, has led to the present view that the central complex was most likely an ancient Buddhist temple.
Scale and Layout of the Archaeological Site
Jusanpozuka Ruins cover an area approximately 390 meters from north to south and more than 200 meters from east to west.
The western and southern sides were enclosed by a substantial ditch approximately 4.7 meters wide and 2 meters deep. On the eastern side, a natural valley served as part of the site’s boundary.
The ancient Tosan-do Station Route ran along the northern side of the site. After the route was changed, its roadside drainage ditch was reused as an irrigation channel. Known as Ushibori, this waterway remains an important reminder of ancient civil engineering and water-management techniques.
The Central Temple Complex
Near the northern-central part of the site is the main temple precinct, surrounded by the remains of a cloister. The enclosed area has an irregular quadrilateral shape, measuring approximately 90 meters along the eastern side, 82 meters along the south, 85 meters along the west, and 70 meters along the north.
At the center of the cloister is a raised foundation measuring approximately 20 meters east to west and 16 meters north to south. Archaeologists believe that a building measuring three bays across the front and two bays in depth once stood on this foundation.
This structure is believed to have been the temple’s Kondo, or Main Hall, where Buddhist images and important religious ceremonies would have been housed.
Pagoda and Temple Gate
To the southwest of the Main Hall foundation is a square foundation approximately 12 meters on each side. This is believed to have been the foundation of the temple’s pagoda.
A gate was also discovered along the southern side of the cloister. Its construction included supporting posts both in front of and behind the main pillars, forming a substantial four-legged gate.
Buildings Surrounding the Temple
Numerous buildings were concentrated to the east of the cloister. Archaeological investigations have identified approximately 30 post-built structures and around 50 pit dwellings.
The buildings were arranged in an orderly fashion and appear to have been divided into three separate blocks. They may have served as residences for monks, facilities for managing the temple, workshops, or other support buildings.
The organized arrangement resembles that of ancient government administrative complexes, which helps explain why the site was once considered a possible district government office.
Valuable Artifacts Discovered at Jusanpozuka
A wide variety of artifacts have been recovered from Jusanpozuka Ruins, providing valuable information about ancient Buddhist culture, craftsmanship, and everyday life.
In particular, the large quantity of Buddhist-related objects provides important evidence that the site functioned as a temple.
Buddhist Artifacts
Important discoveries include fragments of clay sculptures of Buddhas, embossed bronze Buddhist images, animal-shaped legs from a Nara Sansai incense burner, three-color glazed bowls, gray-glazed ritual vessels, and ceramic pagodas.
The embossed Buddhist images were made by placing a bronze plate over a mold and hammering it into shape. These objects demonstrate the sophisticated Buddhist artistic traditions that had reached the region during the Nara period.
Taken together, the discoveries suggest that the area had become an important center of Buddhist worship and culture during ancient times.
Connection with the Provincial Kokubunji Temple
The roof tiles discovered at Jusanpozuka were produced at the Kasakake Tile Kilns. Archaeologists have found that some of these tiles were made using the same molds as tiles used at the Ueno Kokubunji Temple, the provincial Buddhist temple of ancient Ueno Province.
Based on this evidence, the foundation of the Jusanpozuka temple is believed to date to the Tenpyo-Shoho era, around 749–757.
One theory suggests that the temple may have been the ujidera, or clan temple, of the Hinokuma clan, a local powerful family involved in the construction of Ueno Kokubunji.
During ancient times, local aristocratic families and district administrators played important roles in the construction and management of provincial temples. Jusanpozuka may therefore have been established as part of the same religious and political development surrounding the provincial Kokubunji system.
Roof Tiles Bearing Ancient Place Names
Some of the roof tiles discovered at the site bear inscribed characters. These are especially valuable because they provide clues about the administrative divisions and communities of ancient Ueno Province.
The characters “Sa,” “Fuchi,” “Tan,” and “Sasa” have been identified on the tiles. They are believed to refer to ancient place names within Sawi District of Ueno Province, including Sawi-no-Go, Fuchina-no-Go, Tanji-no-Go, and Sasabe-no-Go.
Such inscribed roof tiles are important archaeological sources for understanding the administrative organization and local communities of ancient Japan.
A Temple and Center of Ancient Industry
Jusanpozuka was not only a religious site. Archaeological evidence also indicates that various forms of production and manufacturing took place here.
Numerous artifacts associated with metalworking and lacquer production have been discovered, suggesting that the site also functioned as an important center of ancient industry.
Evidence of Metalworking
Among the discoveries are iron slag, the waste produced during ironworking; tuyeres, or pipes used to supply air to a furnace; ladles for handling molten metal; crucibles; molds; and fragments of furnace walls.
These finds indicate that workshops capable of producing cast iron and cast bronze operated within the site.
Evidence of Lacquer Production
Many pieces of pottery bearing traces of lacquer have also been recovered. This suggests that a lacquerware workshop may have operated at the site as well.
The combination of a Buddhist temple, residential facilities, and specialized workshops demonstrates that Jusanpozuka was more than a place of worship. It appears to have played a broader role as a center of religion, production, and regional activity.
An Important Window into Ancient Ueno Province
Jusanpozuka Ruins provide a valuable picture of political, religious, and industrial life from the Nara to Heian periods.
The remains of the Buddhist temple, the organized arrangement of buildings, and the wide variety of artifacts allow visitors and researchers to imagine how local society functioned more than a thousand years ago.
The site’s location near the ancient Tosan-do Station Route, together with the discovery of roof tiles connected to Ueno Kokubunji, also suggests that this part of Isesaki was an important center within ancient Ueno Province.
Today, Jusanpozuka Ruins are preserved as a National Historic Site and remain an important cultural heritage site for learning about the ancient history of the Isesaki area. Along with the many kofun and other archaeological remains found around Isesaki, the ruins form an important part of the region’s ancient heritage.