Complete Guide to Koshinozuka Castle (Sakura City, Chiba Prefecture) | A Thorough Explanation of the Castle Ruins Associated with the Koga Shogun
What is Koshinozuka Castle?
Koshinozuka Castle is a medieval castle site located in Koshinozuka, Sakura City, Chiba Prefecture. Built on a plateau on the right bank of the Kashima River, this castle has deep ties to the Chiba clan and is known as the place where Ashikaga Shigeuji, the first Koga Shogun, resided for a time after being driven out of Koga Castle during the Kyotoku Rebellion in the Muromachi period.
Currently, it is maintained as the “Koshinozuka Castle Ruins Park” within the grounds of Shokeiji Temple and is designated as a historical site of Sakura City. The remains, such as earthworks and moats, are well-preserved, making it a valuable historical site for learning about the structure of medieval castles.
History of Koshinozuka Castle
Construction Period and Early History
The exact construction date of Koshinozuka Castle is not clearly known. However, it is known that this region was the territory of the Into clan from the Heian period to the early Kamakura period. Later, the Hirakawa and Shishikura clans, direct vassals of the Chiba main family, came to possess the territory.
Given its close ties to the Chiba clan, it is believed to have been built as the Chiba clan expanded its power, although no definitive records remain. Considering the castle’s location, it is presumed to have played a role in controlling a key transportation point in the Kashima River basin.
The Move of Ashikaga Shigeuji, the Koga Shogun
The most important event in the history of Koshinozuka Castle is the move of Ashikaga Shigeuji, the Koga Shogun. In 1471, after being driven out of Koga Castle during the Kyotoku Rebellion, Ashikaga Shigeuji sought refuge with Chiba Takatane, the head of the Chiba clan, and established his residence at Koshinozuka Castle.
Shigeuji stayed at this castle for approximately two years, observing the political situation in the Kanto region. During this period, Koshinozuka Castle temporarily became the political center of the Kanto region and played an important role. The fact that a high-ranking figure, the Koga Kubo (governor of Koga Province), stayed at this castle is evidence of the Chiba clan’s power and the importance of Koshinozuka Castle at the time.
Stay of Ashikaga Masauji and Takamoto
Approximately 30 years after Ashikaga Shigeuji’s arrival, in 1502 (Meiō 11), Ashikaga Masauji, the Koga Kubo, and his son Takamoto also stayed at Koshinozuka Castle. Their stay is believed to have lasted approximately three years.
The fact that the Koga Kubo used Koshinozuka Castle as their base on two occasions indicates that it was an important base for the Chiba clan in the Kanto region. It also demonstrates the strong relationship between the Chiba clan and the Koga Kubo.
After the Sengoku Period
Details about Koshinozuka Castle after the Sengoku period are scarce, and many points remain unclear. It is believed that as the Chiba clan’s power declined, the castle’s function as a castle gradually diminished. During the Edo period, the castle ceased to function as a fortress and was left neglected as a wooded area for a long time afterward. The castle site became part of the grounds of Shōei-ji Temple and has been managed by the temple to this day.
Structure of Koshinozuka Castle
Location and Layout
Koshinozuka Castle is a flatland castle built on a river terrace on the right bank of the Kashima River. It was constructed utilizing the slightly elevated terrain at the southern end of the plateau, making it a typical example of a medieval castle that skillfully utilizes natural topography.
The castle’s elevation is approximately 28 meters, with a relative height difference of about 18 meters from the surrounding area. This difference in elevation served as a natural defensive line, making enemy intrusion difficult. The flow of the Kashima River also functioned as a natural moat, further enhancing the castle’s defensive capabilities.
Main Enclosure (Honmaru)
The main enclosure, the central part of Koshinozuka Castle, is located at the highest point of the plateau. Currently, the main hall of Shōei-ji Temple and other buildings stand on the site, making it difficult to completely restore its original appearance. However, the layout of the surrounding earthworks and moats allows us to estimate its scale.
A moat is positioned on the north side of the main enclosure, clearly defining the boundary. This moat remains well-preserved, and its depth and width provide insight into the defensive structure of the time. Access to the main enclosure was limited, indicating a design that prioritized defense.
Earthworks and Moats
The greatest highlight of Koshinozuka Castle is its well-preserved earthworks and moats. The earthworks surrounding the main enclosure are approximately 2-3 meters high, exhibiting a typical structure of a medieval castle.
The moat is particularly clearly visible on the north side of the main enclosure, measuring approximately 5-8 meters wide and 3-4 meters deep. It is thought to have functioned as a dry moat, an important defensive structure to prevent enemy intrusion.
Based on the layout of the earthworks and moats, it is presumed that the castle was a relatively small structure, perhaps a single or double enclosure. This suggests that it had a strong residential character, and even when the Koga Shogunate stayed there, it is thought to have functioned more as a political center than a large military base.
Layout of Enclosures
Regarding the layout of the enclosures at Koshinozuka Castle, many details other than the main enclosure remain unknown. However, observations of the topography and the distribution of remains suggest the possibility that several secondary enclosures were arranged around the main enclosure.
The area currently maintained as a castle park is limited to the main enclosure and its surroundings, but it is possible that the castle grounds once extended over a wider area. Further research is expected to reveal more details.
Development of Koshinozuka Castle Park
History of Development
The Koshinozuka Castle site was left neglected as a wooded area for a long time, but in 2001, construction to develop it into a castle park was started by Sakura City. This development project led to the excavation of buried remains, clarifying earthworks and moats.
During the restoration work, the preservation of the remains was the top priority, while walking paths and information boards were installed to make it easier for visitors to understand the castle’s structure. Currently, it is used as a valuable educational site for learning about the structure of medieval castles.
Current Visiting Facilities
At Koshinozuka Castle Ruins Park, a parking lot has been developed in the valley on the west side. From the parking lot, a walking path leads up to the moat below the north side of the main enclosure. The walking path is arranged to circle the main parts of the castle, allowing visitors to observe the remains such as earthworks and moats up close.
Explanatory boards are installed within the castle ruins park, providing detailed explanations about the castle’s history and structure. Furthermore, as it is also the grounds of Shōei-ji Temple, visitors can enjoy a unique landscape where temple buildings and medieval castle remains coexist.
Related Historical Sites in the Surrounding Area
Ōshinozuka Castle
Ōshinozuka Castle is located approximately 1.2 kilometers west of Koshinozuka Castle. Ōshinozuka Castle, built on a plateau on the right bank of the Kashima River, is also thought to be a castle associated with the Chiba clan, similar to Koshinozuka Castle.
The distance and location of the two castles suggest they may have played a role in coordinating and defending the Kashima River basin. Visiting Ōshinozuka Castle allows for a deeper understanding of the medieval castle network in this region.
Usui Castle
Sakura City also boasts another famous medieval castle, Usui Castle. Usui Castle was the residence of the Usui clan, a branch of the Chiba clan, and is known for repelling attacks by Uesugi Kenshin during the Sengoku period.
Usui Castle is also designated as a city historical site, and its remains, such as earthworks and moats, are well-preserved. Visiting it along with Koshinozuka Castle allows you to experience the diversity of medieval castles in Sakura City.
Sakura Castle
Sakura Castle is a well-known castle from the early modern period. Sakura Castle originated as a medieval castle built in the mid-Sengoku period by Kashima Mototane, a member of the Chiba clan, and was renovated into a modern castle in the early Edo period by Doi Toshikatsu.
It is now maintained as Sakura Castle Ruins Park and is selected as one of Japan’s Top 100 Castles. You can learn about the history of castle development from the medieval Koshinozuka Castle to the modern Sakura Castle.
Access Information
Access by Public Transportation
If you are visiting Koshinozuka Castle Ruins Park by public transportation, the nearest station is Monoi Station on the JR East Sobu Main Line (including direct service to the Narita Line). From the north exit of Monoi Station, take the Sakura City Community Bus Southern Area Route and get off at the “Koshinozuka Castle Ruins Park” bus stop; you will arrive at the castle ruins park immediately.
Since the number of bus services is limited, it is recommended to check the timetable on the Sakura City website in advance. If using the bus is difficult, you can also take a taxi from Monoi Station.
Access by Car
If you are visiting by car, you can use the Sakura Interchange or Yotsukaido Interchange on the Higashi-Kanto Expressway. From the interchange to Koshinozuka Castle Ruins Park, it takes about 15-20 minutes via local roads.
While there is a dedicated parking lot at the castle ruins park, the road leading to the parking lot is relatively narrow, so caution is required when driving. The parking lot is located in the valley on the west side and has space for several cars.
Location
Address: 598-1 Koshinozuka, Sakura City, Chiba Prefecture (within the grounds of Shoei-ji Temple)
Since the castle ruins park is located within the grounds of Shoei-ji Temple, you must be mindful of the temple’s visiting hours and events. While visits are generally free, please be mindful of proper etiquette and avoid causing inconvenience to the temple.
Points to Note During Your Visit
Observing the Earthworks and Moats
The main highlight of a visit to Koshinozuka Castle is the well-preserved earthworks and moats. The moat on the north side of the main enclosure is particularly clear, allowing you to truly appreciate the defensive structure of a medieval castle. By observing the depth and width of the moat and the height of the earthworks, you can learn about the castle-building techniques of the time.
There are also sections where you can walk on top of the earthworks, offering a panoramic view of the castle’s overall structure. Since the vegetation varies with the seasons, a winter visit is recommended as it makes observing the remains easier.
Understanding the Topography
Koshinozuka Castle is a castle that skillfully utilizes a natural topography: a river terrace. Standing on the edge of the plateau, you can enjoy a panoramic view towards the Kashima River, giving you a real sense of why the castle was built in this location.
Walking around the castle and experiencing the elevation differences helps you understand how the natural terrain was utilized for defense. Especially along the edge of the plateau, the steep slopes served as a natural defensive wall.
Information Boards and Explanations
Information boards installed within the castle ruins provide detailed explanations about the castle’s history and structure. Reading these explanations while exploring will lead to a deeper understanding.
The explanation regarding the relocation of the Koga Shogunate is particularly essential for understanding the historical importance of this castle. We recommend stopping in front of the information boards and taking time to reflect on the history.
Points to Note When Visiting
Clothing and Equipment
While Koshinozuka Castle Ruins Park has well-maintained walking paths, there are also some dirt paths and stairs. Wearing comfortable shoes is recommended. Particular caution is needed after rain, as the ground can become slippery.
During the summer, there may be many insects such as mosquitoes, so consider carrying insect repellent and wearing long sleeves and long pants. Also, since there are few places with shade, bringing a hat and sunscreen is important.
Visitor Etiquette
Since Koshinozuka Castle Ruins Park is located within the grounds of Shōei-ji Temple, it is necessary to maintain the tranquility expected of a temple. Please refrain from loud conversations and noise, and be considerate of other visitors and worshippers.
Furthermore, to protect the historical remains, any actions that unnecessarily damage the earthworks or moats are strictly prohibited. Please refrain from entering areas other than the designated walking paths, and be considerate in order to preserve the historical site for future generations.
Photography
Photography is generally permitted within the castle ruins park, but consideration is required when photographing temple buildings or other worshippers. Photography may be prohibited inside the main hall of the temple, so please check in advance.
Permission from the temple is required for the use of drones and other unmanned aerial vehicles. Please absolutely avoid flying them without permission.
The Chiba Clan and Koshinozuka Castle
History of the Chiba Clan
The Chiba clan was a samurai family that wielded power mainly in Shimōsa Province (present-day northern Chiba Prefecture) from the late Heian period to the Sengoku period. The Chiba clan was a prestigious family descended from the Kanmu Taira clan and held an important position as a gokenin (vassal) during the Kamakura period.
The Chiba clan built many castles within Shimosa Province and governed their territory by stationing family members and retainers there. It is believed that Koshinozuka Castle functioned as part of this Chiba clan castle network.
Chiba Takatane and the Koga Kubo
Chiba Takatane, who welcomed Ashikaga Shigeuji to Koshinozuka Castle in 1471, was the head of the Chiba clan at the time. Takatane valued his relationship with the Koga Kubo and played an important role in the political situation of the Kanto region.
It is believed that the Chiba clan sought to strengthen their position in Kanto by protecting the Koga Kubo. This political decision is considered to have had a certain effect on maintaining the Chiba clan’s power.
Cultural Value of Koshinozuka Castle
Designation as a Sakura City Historic Site
The Koshinozuka Castle ruins are designated as a Sakura City historic site and are protected as an important cultural property of the city. In addition to the well-preserved remains of the medieval castle, its historical importance due to its connection with the Koga Shogunate is highly valued.
The designation as a historical site restricts development of the castle ruins and legally guarantees the preservation of the remains. This makes it possible to pass on this valuable historical heritage to future generations.
Academic Significance
Koshinozuka Castle provides important material for the study of medieval castles. As a typical example of a castle built on a river terrace, it is a valuable case study for learning about castle construction techniques and defensive philosophies.
Furthermore, as the stage for the politically significant event of the relocation of the Koga Shogunate, it occupies an important position not only in the study of castle history but also in the study of medieval political history. It is expected that further historical facts will be revealed through future excavations and research.
Significance of Visiting Kooshinozuka Castle
As a Place for Historical Learning
Koshinozuka Castle Ruins Park is a valuable learning place where you can experience medieval history. Visiting actual castle ruins allows you to concretely visualize the political turmoil of the Muromachi period and the realities of samurai society in the Kanto region, which you learn about in textbooks.
Especially for students and history enthusiasts studying the Kyōtoku Rebellion and the Koga Kubō, this castle site is an excellent opportunity to deepen their understanding. Visiting the site will give you a sense of reality that you cannot get from books alone.
Understanding Local History
Koshinozuka Castle is indispensable for understanding the history of Sakura City and Chiba Prefecture. Visiting this castle allows you to understand the historical changes the region has undergone.
For local residents, it is an opportunity to learn about the historical background of their land, deepening their attachment to their hometown. For visitors from other regions, it will be an opportunity to discover the rich history and culture of Chiba Prefecture.
As part of a Castle Tour
For those who enjoy visiting castles throughout Japan, Koshinozuka Castle is one that should be added to their list. You can feel the simple charm of a medieval castle, different from the famous early modern castles.
Visiting Koshinozuka Castle along with other castle ruins in Sakura City (such as Oshinozuka Castle, Usui Castle, and Sakura Castle) allows for comparative research into the development of castles from the medieval to the early modern period. Castle enthusiasts will find this a fulfilling exploration experience.
Summary
Koshinozuka Castle is a medieval castle site located in Sakura City, Chiba Prefecture. It is known as a castle associated with the Chiba clan and as a historically important castle where the Koga Shoguns Ashikaga Shigeuji, Masauji, and Takamoto stayed. Built on a river terrace on the right bank of the Kashima River, the remains of earthworks and moats are well-preserved.
Currently, it is maintained as the Koshinozuka Castle Ruins Park within the grounds of Shoei-ji Temple and is designated as a historical site of Sakura City. Accessible by public transport and car, it is a valuable educational site for learning about the structure of medieval castles.
Visiting Koshinozuka Castle allows you to gain diverse historical knowledge, including the political turmoil of the Muromachi period, the history of the Chiba clan, and the construction techniques of medieval castles. When you visit Sakura City, be sure to stop by this historic castle ruin.
