The kilns did not appear by accident. This stretch of the Kanna River valley was home to the Hajibe, a hereditary caste of potters whose identity and social standing were defined entirely by their craft. The Hajibe specialized in two products: Haji ware, a practical earthenware used in daily life, and haniwa, the ritual clay figures placed on and around kofun, the massive keyhole-shaped burial mounds built for Japan's ruling elite during the Kofun period. A Shinto shrine still stands nearby, dedicated to the ancestors of the Hajibe clan, a quiet acknowledgment that the people who worked these kilns were not anonymous laborers but skilled artisans with a recognized lineage and spiritual tradition.

Haniwa are among the most distinctive artifacts of ancient Japan. The word itself means "circle of clay," a reference to how the figures were arranged in rings atop burial mounds. Ranging from simple cylinders to elaborate depictions of armored warriors, dancing women, houses, boats, and animals, haniwa served purposes both practical and spiritual. They helped retain the soil of the mound, marked sacred boundaries, and represented a retinue of servants, soldiers, and possessions meant to accompany the deceased into the afterlife. Some scholars believe they replaced an older practice of human sacrifice at royal burials. At the Hongo site, excavators found shards of many haniwa types scattered in front of the kiln area, including horse-shaped figures, evidence that this workshop supplied the full range of funerary forms demanded by the elite across a wide stretch of the Kanto plain.

The kilns themselves were noborigama, climbing kilns that used the natural angle of the hillside to create a draft that pulled flame upward through the firing chamber. Each kiln stretched roughly ten meters in total: a trumpet-shaped ventilation path of about six meters fed into a two-meter cylindrical combustion section, its walls and floor lined with clay to withstand repeated firings. The design was efficient and repeatable, and the tight spacing of the kilns along the cliff face suggests organized, almost industrial-scale production. Academic excavation did not reach the site until 1943, though the kilns' existence had been confirmed as early as 1911. Archaeologists excavated two of the dozen-plus kilns in detail before the site was designated a National Historic Site in 1944 and carefully backfilled to preserve what remained.

The Hongo Haniwa Kiln Site has been buried twice: once by the passage of fourteen centuries, and again deliberately by the archaeologists who uncovered it. After the 1943 excavation documented the kiln structures and collected the scattered haniwa fragments, the site was reburied and returned to forest. Today, the terraced slope above the Kanna River shows little visible trace of the ancient workshop beneath. There are no reconstructed kilns, no dramatic ruins to photograph. The site is a thirty-minute walk from Gunma-Fujioka Station on the JR East Hachiko Line, and what it offers is subtler than spectacle: the knowledge that beneath ordinary-looking ground, the tools of an entire belief system about death and the afterlife were once manufactured at scale, by families who passed their craft from generation to generation for over a century.