Samuraizuka Tomb

Where Japan's Archaeology Began

In the autumn of 1692, workers sent by Tokugawa Mitsukuni, the retired second lord of the Mito domain, climbed a large earthen mound on the right bank of the Naka River in what is now Ōtawara City, Tochigi Prefecture. Following detailed instructions, they cut a shaft about five shaku (roughly 1.5 metres) into the centre of the rear platform. They lifted out stone bracelets, iron arrowheads, tubular jasper beads, and pottery jars. An artist drew every object to scale. The finds were then sealed in pine boxes and reburied, the mound was reshaped, and pine seedlings were planted on the slopes to hold the soil. Three centuries later, that operation is regarded as the first scientifically conducted excavation in Japanese history.

The two tumuli that received this treatment, Kami-Samuraizuka and Shimo-Samuraizuka, still rise from the river terrace in the Yuzukami district. They were designated a National Historic Site in 1951. The pines Mitsukuni ordered have grown into a dark canopy across the summits, and the slight depressions left by his dig remain visible at the centre of each rear platform.

Two Square-Backed Keyhole Mounds

Both tumuli belong to a form called zenpō-kōhō-fun, a keyhole tomb whose front (zenpō) is square and whose rear (kōhō) is also square. This is the rarer cousin of the better-known round-backed keyhole tombs (zenpō-kōen-fun) that defined the imperial mausolea of the Kinai region. The Nasu basin, well to the northeast, kept a distinctly local preference for the square-backed type into the late 4th century, and several examples cluster along the Naka River terrace.

Kami-Samuraizuka, lying to the south, is the larger of the two. Modern surveys give it a total length of 114 metres, with a rear platform some 60.5 metres wide and 11.5 metres high, and a front portion 52 metres wide and 6.5 metres high. Within Tochigi Prefecture, only the Fujimoto-Kannonyama tumulus in Ashikaga (116.5 metres) is longer among square-backed keyholes. Walk roughly 800 metres north and you reach Shimo-Samuraizuka, 84 metres long, with a rear platform 48 metres wide and 9.4 metres high. Despite the smaller scale, this is often described as the most graceful tumulus in Japan, thanks to the cleanly preserved silhouette of its mound. Both were built in the late 4th century, with the upper tumulus probably preceding the lower by a generation. Both originally carried a covering of river cobbles (fukiishi), and traces of the moats that once surrounded them have been confirmed by recent excavation.

The Genroku Excavation

Mitsukuni was not looking for grave goods. He was pursuing a name. In 1683 he had been shown a manuscript called Nasuki by Daigane Shigesada, a village headman in nearby Mumo who would later direct the field excavation. The book described an ancient inscribed stone, the Nasu no Kuni no Miyatsuko stele, that recorded the funeral rites of an early provincial chieftain named Nasu-no-Atai-Ide. Mitsukuni, then immersed in compiling the great chronological history of Japan known as Dai Nihonshi, wanted to identify the chieftain's grave. The two Samuraizuka mounds stood close enough to the stele to be plausible candidates.

No epitaph appeared inside the mounds, and the question of who lies buried there has never been answered. What did emerge was a record. Daigane wrote up the proceedings in a document titled Yuzukami-mura Kuruma-zuka Go-shūri, listing the artifacts and the layer in which each was found. The painter's drawings preserved a visual archive of objects that were then returned to the earth. Mitsukuni's instruction that the finds be reburied, the mound rebuilt, and trees planted to anchor it was a striking break from the casual tomb-opening of his era. The stele itself, meanwhile, was enshrined at Kasaishi Shrine 500 metres north of the lower tumulus, where it remains today and where it was later designated a National Treasure.

What Recent Research Has Found

Modern investigators have returned to the site several times. A 1975 survey of Shimo-Samuraizuka confirmed the fukiishi cobble covering and recovered Haji-ware jars from the moat zone. Beginning in 2021, Tochigi Prefecture and Ōtawara City launched a multi-year programme that combined aerial laser survey, ground-penetrating radar, and targeted excavation of the moat zone. The radar revealed terraced construction not visible from the surface and detected a deep cavity at the centre of the upper mound's rear platform, possibly the original Genroku dig hole, though no metal signature from the buried pine boxes appeared. The moat survey showed that the western ditch of Kami-Samuraizuka had been cleanly cut while the eastern side had been left only roughly levelled, and that the upper fill of the moat had been disturbed once during the Edo period. Mitsukuni's restoration team may have borrowed soil from the ditches to refill the dig shafts and rebuild the summit.

Visiting the Site

The two mounds sit in open countryside, roughly a kilometre apart along Route 294. Both are open to walk around at any hour and entry is free. Pine forests shade the summits, and the path along the base of Shimo-Samuraizuka, which runs beside flooded paddy fields in spring and early summer, gives the clearest view of the keyhole outline. A short walk away on the same plateau, the Otawara City Nasu Fudoki-no-Oka Yuzukami Museum displays material from the wider Nasu region and presents the Mitsukuni excavation alongside the history of the National Treasure stele. Kasaishi Shrine, which houses the actual stele, is a five-minute drive north. For visitors arriving by train, the nearest station is JR Nasushiobara on the Tōhoku Shinkansen, from which a taxi or rental car covers the remaining distance in about thirty minutes.