Ōno Castle: A Korean-Style Mountain Fortress in Japan
Site at a Glance
- Rating
- 4
- Popularity
- Very Low
- Country
- Japan
- Primary era
- Medieval
- Eras represented
- Medieval
- Civilizations
- Yamato
- Site type
- Military
- Remains
- Fort
On this page10 sections
History
Ōno Castle is a Korean-style mountain fortress in Umi, Japan, built by the Yamato court in the seventh century during the Asuka period, an era of early state formation. It was constructed to protect Dazaifu, a major governmental and military center in northern Kyushu, after the defeat of the combined Baekje and Yamato forces by the Silla-Tang alliance at the Battle of Hakusukinoe in 663.
Foundation after Hakusukinoe
The defeat intensified fears that Tang, the Chinese dynasty allied with Silla, or Silla itself might invade the Japanese archipelago. The Yamato court responded by establishing a network of continental-style fortifications. These Korean-style mountain fortresses used extensive ridge-top walls, earthworks, and controlled gates, reflecting defensive systems associated with ancient fortifications on the Korean Peninsula.
The Nihon Shoki, an early Japanese historical chronicle covering events through the seventh century, records construction at Ōno Castle in 665 during the reign of Emperor Tenchi. Much of the work was carried out by people who had fled Baekje, the ancient Korean kingdom that had been an ally of the Yamato court. Construction of related fortifications continued through 701, even after the Silla-Tang War changed the political situation in East Asia.
Use and later development
Ōno Castle was used during the Asuka period. Its initial defensive construction was followed by the addition of later buildings, including structures interpreted as warehouses. A 698 entry in the Shoku Nihongi, a chronicle continuing the historical record into the eighth century, records repairs at the castle. Archaeological investigations also show that the Dazaifu Gate was rebuilt in three stages.
The castle’s name survives in Ōnojō City, whose name derives from Ōno Castle, although about 80 percent of the fortress area lies within Umi Town. The ruins became a National Historic Site in 1932 and a Special Historic Site in 1953. The protected area was expanded in 2012, and the castle was selected among Japan’s Top 100 Castles in 2006.
Damage and archaeological work
Heavy rain in July 2003 caused landslides and the collapse of sections of the earthworks. Restoration work began in 2004 and continued for six years at about 30 locations. The work exposed previously unrecognized rows of stones beneath the earthworks and a line of postholes in front of them. Archaeological excavations continue to develop knowledge of the fortress.
Remains
The ruins occupy Mount Shiōji, formerly called Mount Ōno, at an elevation of 410 meters. The mountain rises behind the ruins of the Dazaifu Government Office on their northern side. The fortress extended about 1.5 kilometers from east to west and three kilometers from north to south. Its horseshoe-shaped defensive line followed the ridge around the summit and reached toward the valley, forming an extensive system of earthworks and stone embankments.
Defensive circuit and valley walls
The outer defensive line extended for approximately 6.8 kilometers toward the valley. Earthworks on the northern and southern sides were doubled, producing a total wall length of about 8.4 kilometers. The surviving circuit makes Ōno Castle the largest ancient mountain castle in Japan. The ruins cross the boundaries of Ōnojō and Dazaifu cities and Umi Town, and nine gate sites have been identified.
Defenses in the valleys included the Hyakken Ishigaki and Mizunote Ishigaki stone walls. Their construction incorporated features for infiltration and natural drainage, while the Tunsui Ishigaki wall contained water outlets. Restoration after the 2003 landslides revealed stone rows along the base of the outer earthworks and postholes positioned in front of them.
Gates and internal buildings
Kita Ishigaki Gate
The Kita Ishigaki Gate had a suspended gate structure and an approximately one-meter step before its entrance. Excavation at the gate produced Japan’s first known bearing-metal fittings for a gatepost, adding physical evidence of the gate’s construction and operation.
Building sites
About 70 building sites have been confirmed in eight locations within the fortress. They include groups supported by standing pillars and buildings set on foundation stones. Some structures with both pillars and foundation stones are interpreted as warehouses and are considered later than the castle’s initial construction. Foundation stones have also been identified with the main castle keep.
Excavated materials and condition
Excavations have recovered inscribed earthenware, roof tiles, and carbonized rice. Together with the building foundations, gates, walls, and earthworks, these materials show the range of construction and activity within the mountain fortress. The remains survive in a ruined condition, with landslide damage forming part of the site’s modern archaeological and conservation history.
