History and Highlights of Oyama Castle (Fukushima Prefecture) | A Southern Court Mountain Castle Built on Mount Shinobu
Oyama Castle, built on Mount Shinobu in Fukushima City, Fukushima Prefecture, is a medieval mountain castle that functioned as a base for the Southern Court during the turbulent Nanboku-cho period. After the death of its lord, Oyama Kurōdo Sadaaki, the castle fell, and although few remains today, it remains an important historical site in the history of Fukushima City.
Overview and Basic Information of Oyama Castle
Oyama Castle was a mountain castle built on Mount Shinobu in Tokoro, Fukushima City, Fukushima Prefecture, located on a hill approximately 50 meters above sea level. The area around the current Shinobu Mountain Second Observatory is thought to be the castle site, a strategically important location offering a panoramic view of Fukushima City.
Basic Castle Data
- Location: Tokoro-kubo, Fukushima City, Fukushima Prefecture (Shinobu-yama)
- Castle Structure: Hill Castle (Mountain Castle)
- Construction Period: Early 14th Century (Estimated)
- Builder: Koyama Kurōdo Sadaaki
- Year of Abandonment: 1358 (Kan’ō 2nd Year / Enbun 3rd Year)
- Remains: Almost completely gone (Only the information board remains)
- Designated Cultural Property: None
Shinobu-yama is a symbolic landmark of Fukushima City and has long been an object of worship. Koyama Castle, built on a corner of this mountain, is an important historical site that tells the story of medieval Fukushima.
History of Koyama Castle
The Turmoil of the Nanboku-chō Period and Koyama Sadaaki
The history of Koyama Castle is closely related to the Nanboku-chō period, a major turning point in Japanese history. In the 14th century, after Emperor Go-Daigo’s Kenmu Restoration failed, Japan was divided into the Southern and Northern Courts, entering a period of turmoil that lasted approximately 60 years.
Oyama Kurōdo Sadatomo was a warrior of the Southern Court who was active in Mutsu Province (present-day Fukushima Prefecture) during this period. Sadatomo built a castle on Mount Shinobu and worked to maintain the Southern Court’s power while confronting the Northern and Ashikaga forces.
The Kannō Disturbance and the Fall of the Castle
The Kannō Disturbance, which began in 1350 (Kannō 1), was a civil war between Ashikaga Takauji and his brother Ashikaga Tadayoshi, further complicating the conflict between the Northern and Southern Courts. During this chaotic period, fierce battles were fought in Mutsu Province.
In 1358 (Kanno 2nd year/Enbun 3rd year), Koyama Kurōdo Sadaaki was killed in battle against enemy forces, and Koyama Castle fell. With Sadaaki’s death, the role of Koyama Castle as a Southern Court stronghold on Mount Shinobu came to an end.
Koyama Castle After its Fall
There are no clear records of what happened to Koyama Castle after its fall. While several castles and fortifications were built around Mount Shinobu during the Sengoku period, there is no evidence that Koyama Castle was reused, and it is believed to have been abandoned.
From the Edo period onward, Mount Shinobu became a mountain of religious significance and a place of relaxation for the people of Fukushima, and the memory of the castle gradually faded.
Layout and Structure of Koyama Castle
Estimated Structure of the Castle
Since no detailed layout map of Koyama Castle remains, and most of the remains have disappeared, it is difficult to know the exact structure of the castle. However, some inferences are possible based on the topography of Mount Shinobu and the characteristics of mountain castles of the same period.
Koyama Castle is classified as a hill castle and was built on a site with a relative elevation difference of approximately 40 meters. It was relatively small for a medieval mountain castle, and it is thought that several baileys (enclosures) were arranged around the main enclosure (honmaru).
Estimated Defensive Structures
In 14th-century mountain castles, the following defensive structures were common:
- Earthwork: An earthen embankment surrounding an enclosure
- Moat: A moat dug to cut across a ridge
- Vertical Moat: A vertical moat dug along a slope
- Enclosure: A flat, leveled area
It is highly probable that these structures were also present at Koyama Castle, but due to changes in the terrain and overgrown vegetation, clear traces cannot be confirmed today.
Strategic Value of the Location
Mount Shinobu is located in the northern part of the Fukushima Basin, offering an excellent location with panoramic views of the surrounding area. From Koyama Castle:
- The flow of the Abukuma River
- The plains of the Fukushima Basin
- The movement of major roads
These factors allowed for monitoring, making it an excellent military base.
Highlights and Current Status of Koyama Castle
Current Situation
Currently, the site of Koyama Castle is believed to be near the Shinobu-yama Second Observation Deck, but no clear remains are left. Almost all traces of the castle have been lost, and only an information board remains.
Shinobu-yama is a recreational area for Fukushima citizens, and the observation deck offers beautiful views of Fukushima city. It is also known as a cherry blossom viewing spot, attracting many visitors in spring.
Information Board
The information board near the castle site concisely describes the achievements of Koyama Kurōdo Sadaaki and the history of the castle. For castle enthusiasts and history buffs, this information board is the only clue.
Other Attractions on Mt. Shinobu
When visiting the ruins of Koyama Castle, we recommend also visiting other attractions on Mt. Shinobu:
Shinobu-yama Park: A representative park of Fukushima City, where you can enjoy nature throughout the seasons.
Haguro Shrine: An ancient shrine located near the summit of Mt. Shinobu, deeply connected to the history of Fukushima.
Observation Decks: There are two observation decks, the first and second, offering magnificent views of Fukushima city and the Azuma mountain range.
Cherry Blossom Viewing Spot: Mt. Shinobu is selected as one of “Japan’s Top 100 Cherry Blossom Viewing Spots,” and boasts approximately 2,000 cherry trees.
Access Information
Access by Public Transportation
From JR Fukushima Station:
- Take the Fukushima Kotsu Bus “Shinobu-yama Loop”
- Get off at “Gokoku Shrine” or “Shinobu-yama Park”
- Approximately 10 minutes on foot to the vicinity of the Second Observation Deck
Access by Car
Tohoku Expressway:
- Approximately 15 minutes from Fukushima-Nishi IC
- Approximately 20 minutes from Fukushima-Iizaka IC
Shinobu-yama Park has several parking lots, which are free to use. However, during peak seasons such as cherry blossom season, the parking lots may be full, so early arrival is recommended.
Estimated Visiting Time
Visiting the Koyama Castle Ruins itself only requires reading the information boards and can be completed in about 10 minutes. However, if you plan to explore the entire Shinobu-yama Park, it is advisable to allow 1 to 2 hours.
Surrounding Castles and Historical Spots
Besides Koyama Castle, many other medieval castles are scattered around Fukushima City.
Fukushima Castle
A flatland castle located in the center of Fukushima City, it was an important base from the Sengoku period to the Edo period. Currently, the site is occupied by the Fukushima Prefectural Government building, and a stone monument remains.
Omori Castle
A medieval castle located in Omori, Fukushima City, and a historical site related to the Date clan.
Iizaka Castle (Tateyama Park)
A mountain castle located near Iizaka Onsen, now developed as a park.
Doai-kan
The remains of a medieval residence located in Matsukawa-cho, Fukushima City, with relatively well-preserved earthworks and baileys.
Reizan Castle (Date City)
A mountain castle used by Kitabatake Akiie during the Nanboku-cho period, and a nationally designated historical site. It is a subject of comparative research as a castle from the same period as Koyama Castle.
Historical Significance of Koyama Castle
Mutsu Province during the Nanboku-cho Period
Koyama Castle is an important historical site that illustrates the complex political situation of Mutsu Province during the Nanboku-cho period. During this period, Mutsu Province was fiercely opposed to the Southern and Northern Courts, and many warlords wavered between the two sides.
The existence of warlords like Koyama Kurōdo Sadaaki, who fought to the end on the Southern Court’s side, is a valuable example that conveys the loyalty and convictions of the samurai of that time.
Position in Local History
In the history of Fukushima City, Koyama Castle played an important role as a medieval military base. Its location on the geographically strategic Shinobu Mountain suggests its involvement in the struggle for control of the Fukushima Basin.
Challenges in Castle Research
Because very few remains of Koyama Castle remain, there are limitations to its study as a subject of castle research. However, through cross-referencing with historical documents and comparative studies with other castles of the same period, a more detailed understanding of its true nature is expected.
Future archaeological excavations may yield new insights.
Points to Note When Visiting Koyama Castle
Precautions When Visiting
- No Remains Exist: Expecting to see traces of the castle may lead to disappointment. It is recommended to visit with an understanding of the historical background.
- Check the Information Boards: The information boards near the second observation deck are the main source of information.
- Wear Comfortable Clothing: While Mount Shinobu is well-maintained, you will be walking on mountain paths, so comfortable shoes such as sneakers are recommended.
- Seasonal Selection: The cherry blossom season (early April) is particularly beautiful, but it gets crowded. For a quieter visit, weekdays or off-season are recommended.
Points for Historical Learning
When visiting Koyama Castle, the following prior learning will deepen your understanding:
- The basic flow of the Nanboku-cho period
- The circumstances of the Kanno Disturbance
- The developments of the Nanboku-cho period in Mutsu Province
- The general structure of medieval mountain castles
Photo Spots
Although there are no remains of the castle itself, the view from Mount Shinobu is magnificent, and you can enjoy taking photos with Fukushima city and the Azuma mountain range in the background. The view at sunset is especially spectacular.
Summary
Koyama Castle was a mountain castle built on Mount Shinobu in Fukushima City, Fukushima Prefecture, during the Nanboku-cho period. The castle lord, Koyama Kurōdo Sadaaki, fought on the side of the Southern Court and was killed in battle in 1358, after which the castle fell. Currently, there are almost no remains left, but an information board has been installed near the Shinobu Mountain Second Observation Deck, allowing visitors to reflect on the history of medieval Fukushima.
While the castle ruins themselves offer limited attractions, Mount Shinobu is a representative scenic spot in Fukushima City and has been developed into a park. It’s also known as a cherry blossom viewing spot, allowing visitors to enjoy the beauty of nature throughout the seasons.
Visiting Koyama Castle allows you to imagine the lives of the warriors who lived during the turbulent Nanboku-cho period and touch upon a part of Fukushima’s history. It’s a historical site worth visiting not only for castle enthusiasts but also for anyone interested in Fukushima’s history.
Why not experience the rich nature and historical background of Mount Shinobu while feeling the spirit of the Middle Ages? Because no remains exist, there’s the added pleasure of using your imagination to picture what it was like back then. When you visit Fukushima City, be sure to stop by the Koyama Castle ruins.
