Funawara Tomb

Funabaru Kofun: A Keyhole Tomb and Its Buried Treasure of Golden Horse Gear

In the spring of 2013, archaeologists working in a quiet stretch of farmland in Koga, Fukuoka Prefecture, opened a narrow pit in the ground and found it packed with horse trappings, weapons, and armor. More than five hundred objects had been laid there roughly fourteen centuries ago, some of them apparently still inside wooden boxes. Several pieces, including a gilt-bronze pendant inlaid with the iridescent wings of jewel beetles, had no parallel anywhere else in Japan.

That pit, and six others beside it, belong to Funabaru Kofun (船原古墳), a burial mound that turned a corner of Koga into one of the most talked-about archaeological sites in Kyushu.

What Funabaru Kofun Is

Funabaru Kofun sits at the tip of a low spur of land, about 40 meters above sea level, looking out toward the Genkai Sea. It is a zenpō-kōen-fun, a keyhole-shaped tumulus combining a round mound with a trapezoidal front, the signature tomb form of Japan's Kofun period. What survives today measures 37.4 meters in length, and researchers estimate the original mound exceeded 45 meters. The round rear section is about 24.8 meters across, edged on its southeast side by a moat 4.4 meters wide.

The burial chamber inside is a corridor-style stone chamber (yokoana-shiki sekishitsu) built from boulders, some close to the size of a tatami mat. It has two connected rooms, an inner chamber and an antechamber. The main chamber is a near-square roughly two meters across with a ceiling around 2.6 meters high, reached through a passage less than a meter wide.

The tomb dates to the late 6th or early 7th century, a verdict supported by the square plan of its chamber and by the Sue ware pottery recovered around it. In northern Kyushu this was the twilight of the keyhole tomb. Within a generation or two the form would vanish, and Funabaru ranks among the very last keyhole tombs raised along the Genkai coast.

The Pits That Changed Everything

The mound itself was first investigated in the 1990s, after farmland improvement work exposed it. At that stage it looked like a modest round tomb. The real surprise came two decades later. During land-readjustment surveys that began in 2012, excavators working five to seven meters southwest of the chamber entrance struck seven Kofun-period pits, aligned with the chamber's opening and untouched by looters.

Pit No. 1 was the richest. Shaped like a reversed letter L, 5.3 meters long and up to 2.3 meters wide, it held the bulk of the haul: harness fittings, lamellar armor, a lacquered wooden bow, iron arrowheads, and farming tools such as a sickle, a spade tip, and an axe. The count passed five hundred items, and the way some lay suggests they had been packed into boxes before burial. The other pits added a large Sue ware jar, ring-form bit fittings, bundles of arrowheads, and more pottery.

Crucially, pottery from several of these pits physically joins with pottery found in the tomb's moat and mound. The fragments fit together, which ties the pits firmly to the tomb itself. Setting a separate cache of grave goods outside the mound, rather than inside the chamber, had never been documented before in Japan. There is no sign that horses were sacrificed and buried with the gear, which makes the deposit harder to explain and all the more interesting.

The Horse Armor and the Jewel-Beetle Pendant

Among the trappings, a handful of pieces lift Funabaru into rare company.

The first is a bachū, a piece of armor that covered a horse's head. It came out of the ground in fragments and was painstakingly reassembled at the Kyushu Historical Museum, where conservators stripped away soil and rust to recover its shape. The finished helmet is 48.5 centimeters long, made from six iron plates riveted together. Before Funabaru, only two had been found in Japan, at the Ōtani Kofun in Wakayama and the Saitama Shōgunyama Kofun in Saitama, and even counting Korean examples the worldwide total is around twenty. The Funabaru piece has features seen on no other: the plates over the nose and eyes are worked into three dimensions, the edges along the muzzle and cheek curve smoothly, and five buckles secured it to the animal's head. Traces of wood stuck to its surface turned out to be Japanese cedar, a species native to these islands, hinting that the box holding the helmet was made locally even if the helmet's design looked abroad.

The second is a gyōyō, an apricot-leaf-shaped pendant that hung from the harness. Its gilt-bronze openwork is backed with the shimmering green wings of jewel beetles, glimpsed through the gaps in the pattern. Jewel-beetle decoration is famous in Japan from the Tamamushi Shrine at Hōryū-ji and from objects linked to the sacred island of Okinoshima, but it had never been confirmed on horse gear here. On the Korean peninsula such pieces appear only in royal-rank tombs of 5th-century Silla, where they adorned the mounts of the highest elite.

Add to these a set of harness ornaments inlaid with green glass, another domestic first, and a serpentine iron implement of a type closely tied to the peninsula, and the assemblage starts to look less like ordinary grave goods and more like a statement of status and connection. Specialists have described the trappings as "national-treasure class," comparing their splendor to the celebrated finds from the National Treasure Fujinoki Kofun in Nara.

Why It Was Designated

Funabaru Kofun became a National Historic Site on October 3, 2016, the first such designation in Koga. The reasoning rests on several pillars. The undisturbed pits offer a rare window onto funerary ritual at the close of the Kofun period, a practice with no clear precedent. The tomb marks the end of the keyhole form in northern Kyushu. And it stands in a stretch of country between the Munakata district and the Fukuoka plain that had produced no keyhole or large round tombs before, suggesting the area gained sudden importance in the late 6th century.

The quantity of imported and import-influenced goods points to a buried figure with access to the highest-quality objects and to links reaching the Korean peninsula and the Yamato court. This is Kasuya country, and the nearby Shikabe-tabuchi site is a leading candidate for the Kasuya no Miyake, a Yamato royal estate recorded in early chronicles. Funabaru helps historians read the politics of a coast where Japan met the continent.

One point worth keeping straight: the designation protects the tomb and its pits as a historic site. The dazzling objects themselves, though widely praised as national-treasure class, are studied and exhibited as excavated material rather than formally designated treasures.

Visiting the Site

Funabaru Kofun opened to the public as an open grassy plaza in April 2018. Interpretive panels explain the tomb and its discoveries, a parking area has been laid out, and a flat ground-level marker traces where the relic pits were found. Set your expectations correctly before you go: the pits have been backfilled for protection and are no longer visible, and the stone chamber is not open. Visitors view the mound's exterior from outside the protective fence rather than entering the tomb. The approach runs along a farm road through a residential and agricultural area, so slow driving and consideration for neighbors are asked of everyone who comes.

To see the actual objects, head for the museums. The Koga City Museum of History, inside the Lead Pas Plaza Koga complex a short walk from Koga Station, presents research results and finds on a rotating basis. The Kyushu Historical Museum, where much of the conservation work was carried out, has staged major exhibitions of the Funabaru trappings, including a landmark show in 2024. Checking current displays before traveling is wise, since the most spectacular pieces move between conservation, study, and exhibition.

Around Koga

Koga lies on the rail line between Fukuoka and the Munakata coast, which makes Funabaru easy to fold into a wider day of history along the Genkai Sea. The obvious companion is Munakata Taisha and its associated sites, inscribed on the World Heritage List as the "Sacred Island of Okinoshima and Associated Sites in the Munakata Region," a tradition rooted in the same sea routes that carried the objects in Funabaru's pits. Fukuoka city, with the Kyushu National Museum a little further afield in Dazaifu, rounds out a route that runs from imported gold harness fittings to the broader story of early exchange between the archipelago and the continent.