Ichinomiya Castle: A Medieval Mountaintop Fortress in Japan
Site at a Glance
- Rating
- 4
- Popularity
- Low
- Country
- Japan
- Primary era
- Early Modern
- External website
- Open
- Eras represented
- Early Modern
- Civilizations
- Toyotomi regime
- Site type
- Military
- Remains
- Castle
On this page11 sections
History
Ichinomiya Castle is a Japanese mountaintop fortress in Tokushima, founded in 1338 by the fourth son of the Ogasawara governor of Awa during the Nanboku-cho period, the fourteenth-century conflict between rival Northern and Southern Imperial Courts. After defeating Ichinomiya Muneshige, its founder moved to the site, enshrined a divided spirit of Ichinomiya Shrine within the castle, and adopted the Ichinomiya name. The family thereafter held the castle and apparently also served as shrine clergy, joining political, military, and religious authority in one local lineage.
Foundation and the Nanboku-cho Conflict
The founder supported the Southern Court, led by Emperor Go-Daigo in opposition to the Northern Court associated with Ashikaga Takauji, founder of the Muromachi shogunate. In 1340, forces serving the Hosokawa family subdued nearby strongholds and concentrated their attack on Ichinomiya Castle. After the founder died, Hosokawa forces burned the settlement around the castle in 1350. This was the first recorded battlefield use of the fortress.
Fighting continued until the Ichinomiya lord was defeated by the Hosokawa in 1362. He made peace with them, transferred the castle to his son, and retired to another stronghold. His successor submitted to the Northern Court and became a Hosokawa vassal. Members of the Ichinomiya family later served among the local warriors repeatedly sent to the Kinai, the central region around Kyoto and Osaka, during internal struggles within the Hosokawa house.
Hosokawa and Miyoshi Rule
During the sixteenth century, the Miyoshi family displaced the Hosokawa as rulers of Awa. The Ichinomiya family responded by forming a marriage alliance with the Miyoshi, and under its twelfth lord it held an important position among Miyoshi retainers. This relationship later became strained when conflict within the Miyoshi regime drew the Ichinomiya lord toward the opposing Hosokawa faction.
He raised troops in support of Hosokawa Masayuki and surrounded the Miyoshi army at Imakiri Castle for three days. When the Miyoshi commander escaped, the Ichinomiya lord pursued him, and the commander committed suicide. The destruction of the supporting forces then left Ichinomiya exposed. He sought an alliance with Chosokabe Motochika through a relative of the Chosokabe family. The Chosokabe were a powerful warrior house competing with the Miyoshi for control of Awa and other parts of Shikoku.
Sieges and the Chosokabe Conquest
Motochika invaded Awa and captured Onishi Castle. The Ichinomiya lord later advanced toward Shozui Castle, but contrary advice caused him to turn back. On the return journey he defeated an attack by troops from Awaji. An army of about 7,000 men, reinforced from Kii and Awaji, then besieged Ichinomiya Castle, forcing the lord to withdraw to Shosanji Temple. He returned after the Miyoshi commander was defeated below Waki Castle.
In 1580, the Ichinomiya lord tried to drive the Miyoshi commander toward another castle. The commander escaped, and Ichinomiya then took Shozui Castle. Miyoshi forces recovered it in 1581 and attacked Ichinomiya Castle, but the defenses held. The siege ended when a Chosokabe relief force of more than 20,000 cavalry was reported to be approaching.
In 1582, after Oda Nobunaga’s plans to expand into Shikoku collapsed, Motochika invaded and unified Awa after defeating the Miyoshi at the Battle of Nakotomigawa. The Ichinomiya lord had fought there as the leading commander of the Tosa forces. Motochika later lured him to another castle by promising discussions about rewards and killed him in an ambush. He subsequently eliminated other Awa warlords whom he considered potential threats.
Toyotomi Occupation and Abandonment
Motochika enlarged Ichinomiya Castle by adding a South Castle. He appointed one retainer to command the new section, another to serve as castellan of the older North Castle, and stationed a large garrison. In 1585, Toyotomi Hideyoshi’s campaign against Shikoku brought the castle into one of the principal theaters of operations. Toyotomi Hidenaga, Hideyoshi’s younger half-brother and a senior commander, besieged it with approximately 40,000 troops, while around 10,000 defenders held the fortress. The castle surrendered in late July.
After Motochika submitted to Hideyoshi, Hideyoshi assigned Awa to Hachisuka Iemasa in September 1585. Iemasa made Ichinomiya Castle his residence and extensively remodeled it. He moved to the newly built Tokushima Castle in 1586 and appointed Masatada Masuda as castellan at Ichinomiya, which then became one of nine subsidiary castles supporting Tokushima Castle.
The castle was abandoned in 1638 under the one-domain-one-castle policy, a Tokugawa restriction intended to limit each feudal domain to one principal castle. A local tradition holds that some of Ichinomiya’s stone was carried to Tokushima Castle for repairs. Ichinomiya Castle became a Tokushima Prefectural Historic Site in 1954 and forms part of Higashiryuo Prefectural Natural Park. In 2017, it was selected as site 176 in Japan’s Continued Top 100 Castles and was also designated a Tokushima Civic Heritage site.
Remains
Mountain Fortress and Castle Plan
Ichinomiya Castle occupies the tip of a branch ridge extending northeast from Mount Higashiryuo. The main enclosure stands at 144.3 meters above sea level, about 120 meters above the mountain foot, with steep slopes descending below its stone walls. The Ayukui River to the north and the Funato and Sonose rivers to the east formed natural defensive barriers, while the Shikoku Mountains lay behind the fortress.
The castle consisted of a North Castle and a South Castle. The main enclosure belonged to the North Castle, while Myojinmaru and other enclosed terraces formed part of the South Castle. The whole complex extended approximately 800 meters from east to west and 500 meters from north to south. Its enclosed areas included Saizomaru, Myojinmaru, Oguramaru, Shiimaru, and Mizunotemaru, as well as former storehouse, field, and reservoir areas. A record compiled in 1817 counted six principal baileys, or enclosed castle areas, and thirteen when smaller enclosures were included.
Defenses combined stone walls with earthen ramparts, dry moats, ditches running down slopes, ditches cut across ridges, small baileys, and protected reservoirs. The principal baileys had simple level entrances. No square or offset entrance structures have been identified, suggesting an earlier arrangement than the more developed entrance systems of early-modern castles. No roof tiles have been excavated, so the buildings may generally have had board roofs rather than tiled ones.
North Castle and Main Enclosure
The main enclosure occupies the highest point and is the only enclosure surrounded by stone walls. It measures about 36 meters along its northeastern side and 23 meters along its northwestern side. The walls vary in height, reaching approximately 5 meters on the east, while steep slopes form much of the enclosure’s remaining boundary. A single entrance on the east opens where the ground drops slightly and may have contained a gate tower. There is no separate platform for a keep, but foundation stones south of the enclosure suggest that a building serving an equivalent purpose may once have stood there.
The stone walls are attributed to Hachisuka Iemasa’s remodeling. They use rough-stone masonry, in which irregular stones are laid without regular courses, made from locally abundant crystalline schist. Tall upright stones reinforce the corners. The entrance stairs, foundation stones, and masonry at Kamadoko Bailey are considered parts of the same construction phase. Kamadoko lies one level below the western side of the main enclosure. The main-enclosure walls were repaired by Tokushima City in spring 1986.
Southern Defensive Enclosures
Oguramaru lies south of the main enclosure at an elevation of 123.4 meters. This elongated bailey protected the southern approach and retains an earthen rampart about 2 meters high along its southwestern side. The rampart curves with the terrain and measures roughly 58 meters along its inner face. It has one central entrance. A turret platform projects from its northwestern side. Although now collapsed, the platform is thought to have been square with projecting corners. Outside the rampart, a dry moat also served as a lateral passage and connected with the southwestern entrance, creating opportunities for attacks from the moat, rampart, and turret platform.
Shiimaru and Mizunotemaru were arranged around the former reservoir and protected by earthen ramparts, vertical ditches, and ditches cut across the ridges. Shiimaru, the smallest of the six principal baileys, measures approximately 20 meters from east to west and 20 meters from north to south. Both enclosures have entrances facing toward the main enclosure. Oguramaru, Shiimaru, and Mizunotemaru once formed a horseshoe-shaped enclosure around a large reservoir, with smaller baileys linking them. Although the reservoir embankment has been cut, its former position remains a major part of the water-defense system associated with the castle’s resistance to Hidenaga’s assault.
Approach and Upper Enclosures
Saizomaru, also called the Third Bailey, was the first major enclosure reached by the approach from Ichinomiya Shrine. At 129.2 meters above sea level, it follows the ridge’s natural form in an irregular, elongated east-west shape. Its interior slopes slightly eastward rather than forming a completely level platform. One entrance lies at the western end beside a ditch cut across the ridge. A lower enclosure occupies the eastern end, while another ridge-cut ditch on the northern ridge helped block movement along the ridgeline.
Myojinmaru, or the Second Bailey, stands northeast of the main enclosure at 140.9 meters, about 3.4 meters lower than it. A narrow, belt-shaped bailey, meaning a defensive terrace along the edge of a larger enclosure, almost surrounds Myojinmaru. A dry moat and stepped baileys protect its northern side, and two parallel dry moats defend the northwest. Foundation stones and a raised base survive in the southwestern part. Tradition associates the enclosure with worship directed toward Mount Tsurugi, and these remains are interpreted as evidence for a building with a formal worship hall and main sanctuary.
A leveled belt-shaped enclosure, 64 meters long and 13 meters wide, linked Myojinmaru with the main enclosure. A single stone-stepped entrance on its southern side led into the terrace, which formed an important defense for the main enclosure. A ditch-bottom route between Saizomaru and Myojinmaru led toward this entrance, exposing intruders to attacks from higher baileys. A vertical ditch narrowed part of the route and slowed movement. Other approaches, including the route toward Myojinmaru’s entrance, were similarly overlooked from higher ground.
Storehouses, Waterworks, and Lower Residence
The South Castle included a Storehouse Bailey at 89.7 meters above sea level. It occupies a lightly modified natural ridge rather than a completely level platform, and excavations recovered carbonized grain. Water installations included the former large reservoir, a dry well below the main enclosure, and traces of springs around Saizomaru. The date of the spring traces is uncertain, but the castle area contained numerous small water sources.
The principal entrance probably differed from the present mountain path. The presumed main route ran through Tenmadani Valley, where its entrance and the Kitamachi area contained stepped level spaces interpreted as retainers’ residences. In better-preserved sections, the route is about 2 meters wide and broader than the modern path. Farther up the valley, it divided toward the eastern and western Storehouse Baileys and may also have carried supplies. The rear entrance was probably on the ridge extending south opposite the main approach, while other routes served sorties and withdrawals.
Approximately 500 meters northeast of the main enclosure, at an elevation of about 18 meters, lies the former residential compound. Its area is uncertain but is estimated at roughly 140 meters from north to south by 130 meters from east to west. A shrine now stands within the area, which has become rice paddy. The compound is thought to have been enclosed by a moat and earthen rampart, although those defenses no longer survive. An account of an attack on the Ichinomiya lord’s lower residence is interpreted as referring to this compound and its former defenses.
No reconstructed buildings stand at Ichinomiya Castle. The surviving remains include baileys, stone walls, earthen ramparts, ditches, foundations, stairs, reservoir and well remains, and other archaeological features that preserve the fortress’s layered defensive plan.
