Tamanawa Castle (Kamakura City, Kanagawa Prefecture): A Thorough Explanation of the History and Highlights of the Impregnable Castle Built by Hojo Soun
Tamanawa Castle (Tamanawa-jo) was a hilltop castle located in the Tamanawa area of Kamakura City, Kanagawa Prefecture (formerly Tamanawa Village, Kamakura District, Sagami Province). It is also known as Amanawa Castle. It is known as a castle built by Hojo Soun, who aimed to conquer the Kanto region during the Sengoku period, and was an important base for the Later Hojo clan’s rule of Sagami Province. Currently, the “Tamanawa Castle Site” is designated as a special green space preservation area, recognizing its historical value.
Overview and Location of Tamanawa Castle
Tamanawa Castle was built on a hill approximately 80 meters above sea level, about 1 kilometer northwest of JR Ofuna Station. While the current Tamanawa area of Kamakura City is being developed as a residential area, remnants and historical sites that retain the atmosphere of the time are scattered around the castle site.
The castle’s location was strategically excellent, controlling the entrance to the Miura Peninsula while also functioning as a northern defense line for Kamakura. Furthermore, its strategic location on the route from the center of Sagami Province to the Tokyo Bay coast made it an indispensable base for the Later Hojo clan’s control of Sagami.
History of Tamanawa Castle
Hojo Clan Era: From Construction to Development
Construction by Hojo Soun (Eisho 9, 1512)
Tamanawa Castle was built in Eisho 9 (1512) by Hojo Soun (Ise Sozui), a Sengoku daimyo who sought to expand his influence into the Kanto region. At that time, the Ogigayatsu Uesugi clan and their senior retainer, the Miura clan, held power in Sagami Province, with the Miura clan, based on the Miura Peninsula, being the most powerful force in Sagami Province.
Soun built Tamanawa Castle as a base for his campaign against the Miura clan and appointed his second son, Hojo Ujitoki, as the first lord of the castle. This castle is believed to have served not only as a base for invading the Miura Peninsula, but also as a means of bringing Kamakura under its control.
Conflicts with the Miura Clan
After the construction of Tamanawa Castle, fierce battles raged between the Hojo clan and the Miura clan. In 1516, Miura Yoshitomo (Dosun) attacked Tamanawa Castle, but was unable to capture it due to its strong fortifications and the skillful defenses of Hojo Ujitoki.
Ultimately, in 1526, the Miura clan was destroyed at Arai Castle (Miura City), and the Later Hojo clan established control over the entire Sagami Province. Tamanawa Castle played a crucial role in this process, establishing its reputation as an “impregnable fortress.”
The Era of the Tamanawa Hojo Clan
The lords of Tamanawa Castle were successively appointed from among the close relatives of the Later Hojo clan. These lords were known as the “Tamanawa Hojo clan” and were treated as an important branch of the Later Hojo clan.
Following the first lord, Hojo Ujitoki, the castle lordship was passed down to his son, Hojo Tamemasa, and then to his son, Hojo Ujishige. The Tamanawa Hojo clan were not merely local castle lords, but played a central role in the military and political affairs of the Later Hojo clan.
1590 (Tensho 18): Toyotomi Hideyoshi’s Siege of Odawara
In 1590 (Tensho 18), Toyotomi Hideyoshi launched his siege of Odawara. At this time, the lord of Tamanawa Castle was Hojo Ujikatsu. As Hideyoshi’s large army advanced into the Kanto region, many of the Later Hojo clan’s branch castles fell one after another. However, Tamanawa Castle was known as a strong fortress, and Hideyoshi’s army avoided a frontal assault.
Persuasion efforts by Tokugawa Ieyasu’s senior retainers, such as Honda Masanobu, led to Hojo Ujikatsu’s eventual surrender. As a result, Tamanawa Castle escaped destruction during the battle and was able to maintain its function as a fortress afterward.
Tokugawa Era: The Tamanawa Jinya Era
Honda Clan Era
After the Siege of Odawara, when Tokugawa Ieyasu entered the Kanto region, Tamanawa Castle came under the control of the Tokugawa clan. In 1602 (Keicho 7), Honda Masashige, the second son of Honda Masanobu, was appointed lord of Tamanawa Castle and was granted a fief of 16,000 koku.
The Honda clan used Tamanawa Castle as their residence, but in the peaceful Edo period, the role of the medieval mountain castle gradually changed.
Nagasawa Matsudaira Clan Era (Tamanawa Jinya Period)
In 1634 (Kanei 11), after the Honda clan was transferred, the Nagasawa Matsudaira clan took control of Tamanawa. During this period, the castle transformed into a form known as the “Tamanawa Jinya,” with emphasis shifting from the main keep at the mountaintop to a more residential area at the foot of the mountain.
The Nagasawa Matsudaira clan ruled Tamanawa until the end of the Edo period, and were responsible for the local administration. After the Meiji Restoration, the Tamanawa Jinya (fortified residence) was abolished, and the castle site was sold to private individuals.
Structure and Layout of Tamanawa Castle
Basic Structure of the Castle
Tamanawa Castle is a hilltop castle characterized by its layout that skillfully utilizes the hilly terrain. The main keep (Honmaru) was at the center, with the second and third baileys (Ninmaru and Sannomaru) arranged around it, creating a structure where multiple baileys were connected in a stepped fashion.
The castle grounds extended approximately 500 meters east-west and 700 meters north-south, boasting a considerable scale for its time. In particular, the area around the main keep was protected by steep terrain and deep moats, making it an extremely difficult fortress to attack.
Defensive Facilities
Tamanawa Castle’s defenses made maximum use of the natural terrain. The steep slopes of the hill itself served as defensive walls, further enhanced by artificial cliffs and earthworks.
Access to the castle was limited, and the winding slope known as “Nanamagari-zaka” (Seven-Bend Slope) was a crucial defensive line that slowed down enemy advances. Parts of this slope still remain today, allowing us to imagine the castle’s structure at the time.
Suwa-dan and Taiko-yagura (Drum Tower)
Within the castle grounds was a bailey called “Suwa-dan,” where a Suwa Shrine was enshrined. The remains of a Taiko-yagura (drum tower) have also been confirmed, believed to have functioned as a facility for broadcasting the time and warnings within the castle.
These facilities indicate that Tamanawa Castle was not merely a military facility, but functioned as the center of the entire region, including the castle town.
Remains and Current State of Tamanawa Castle
Honmaru Site (Seisen Girls’ Junior and Senior High School)
Currently, Seisen Girls’ Junior and Senior High School stands on the site of Tamanawa Castle’s Honmaru, and public access is restricted. While there are monuments and explanatory signs marking the castle site on the school grounds, permission from the school is required for visits.
From the site of the main keep, it is said that one could once see Sagami Bay and Mount Fuji, highlighting the castle’s advantageous location. Even today, the surrounding hills offer panoramic views of the vast landscape of Sagami Province.
Nanamezaka Slope
Nanamezaka Slope, the main access route to Tamanawa Castle, still remains in part. Along the road from Ryuhōji Temple towards Seisen Girls’ Academy, you can see the winding slope that retains its original character.
As its name suggests, Nanamezaka Slope winds and bends repeatedly as it ascends to the castle’s higher ground, making it an important historical site that demonstrates the castle’s defensive ingenuity.
Earthworks and Moats
Traces of earthworks and moats can be found in multiple locations around the castle site. In particular, the terrain around the main keep shows signs of artificial modification, providing clues to the castle’s structure at the time.
Even in today’s residential area, careful observation can reveal traces of the castle in the topography’s undulations and elevation changes. ### Megaliths and Stone Monuments
At the Tamanawa Castle ruins, several stone monuments and information boards have been erected to tell the history of the castle. Furthermore, Ryūhōji Temple houses a megalith believed to be part of the Tamanawa Castle remains, providing valuable information for understanding the castle’s building materials and structure.
These stone structures indicate that Tamanawa Castle was not merely an earthen castle, but a sturdy structure built with stone.
Nearby Historical Sites and Points of Interest
Ryūhōji Temple (Family Temple of the Tamanawa Castle Lords)
Ryūhōji Temple is known as the family temple of the Tamanawa Hōjō clan and is located very close to the Tamanawa Castle ruins. The temple grounds contain the tombs of successive generations of the Tamanawa Hōjō clan, including Hōjō Ujitoki, making it an important place to reflect on the castle’s history.
The temple gate dates back to the early Edo period and is a valuable structure that conveys the atmosphere of Tamanawa at that time. Information boards about Tamanawa Castle are also installed on the temple grounds, making it an ideal starting point for a tour of the castle ruins. ### Tamanawa History Museum
Located within walking distance of Ofuna Station, the Tamanawa History Museum is a facility where you can learn about the history of Tamanawa Castle and the Tamanawa region. The museum displays a reconstructed diorama of Tamanawa Castle, allowing visitors to visually understand the castle’s overall structure.
It also exhibits artifacts unearthed during archaeological excavations and materials related to the Tamanawa Hojo clan. When visiting the Tamanawa Castle ruins, it is recommended to first gain some background knowledge at this history museum.
Suwa Shrine
The Suwa Shrine, which originated from the Suwa-dan (a platform for worshippers) located within Tamanawa Castle, continues to be revered as the guardian shrine of the Tamanawa region. It is said that the castle lord prayed for victory at this shrine, and it is deeply connected to the castle’s history.
From the shrine grounds, you can see part of the Tamanawa Castle ruins, making it a useful place to understand the castle’s location and topography.
Nagaya-mon (Former Ishii Residence)
In the Tamanawa region, there are still nagaya-mon (long gatehouses) that retain the appearance of samurai residences from the Edo period. This is a valuable structure that conveys the appearance of the samurai residences during the Tamanawa Jinya era, allowing visitors to experience the atmosphere of a castle town.
Branch Castles (Fortresses) of Tamanawa Castle
Tamanawa Castle did not exist in isolation, but was the center of a castle network with several branch castles and fortresses located around it. These branch castles expanded Tamanawa Castle’s defensive sphere and played a role in monitoring and defending the Miura Peninsula and Kamakura areas.
Notable branch castles include Fukazawa Castle and Kajiwara Castle, which formed a defensive line centered on Tamanawa Castle. While many of these branch castle sites are now residential areas, traces of their existence remain in place names and topography.
List of Successive Castle Lords
Castle Lords during the Later Hojo Clan Era
- Hojo Ujitoki (c. 1512–1524): First castle lord, second son of Hojo Soun
- Hojo Tamemasa (c. 1524–c. 1552): Son of Ujitoki
- Hojo Ujishige (c. 1552–1574): Son of Tamemasa
- Hojo Ujishun (1574–1578): Son of Ujishige
- Hojo Ujikatsu (1578–1590): Second son of Ujishige, castle lord during the Siege of Odawara
The Tamanawa Hojo clan was positioned as a particularly important family within the Later Hojo clan, maintaining close ties with Hojo Ujiyasu and Ujimasa of Odawara Castle, and was responsible for governing the eastern part of Sagami Province.
Lords of Castles and Fortifications during the Tokugawa Period
- Honda Masashige (1602-1619): Second son of Honda Masanobu, 16,000 koku
- Honda Masakatsu (1619-1634): Son of Masashige
- Matsudaira Masatsuna (1634-1638): Nagasawa Matsudaira clan, 23,000 koku
Then, the Nagasawa Matsudaira clan ruled Tamanawa until the end of the Edo period. In the late Edo period, it continued to exist as the Tamanawa Domain, a small domain with a stipend of approximately 16,000 to 20,000 koku.
Access and Visiting Information for Tamanawa Castle
Transportation Access
Access by Train
- Get off at Ofuna Station on the JR Tokaido Line, Yokosuka Line, or Shonan Shinjuku Line, then walk for approximately 15 minutes.
- You can also take a bus from the west exit of Ofuna Station towards the Tamanawa Castle ruins.
Access by Car
- Approximately 10 minutes from the Hino Interchange on the Yokohama-Yokosuka Expressway.
- Parking: Visitor parking is available at Ryuhōji Temple (limited spaces).
Points to Note During Your Visit
Recommended Visiting Route
- Gain background knowledge at the Tamanawa History Museum
- Visit the tombs of the Tamanawa Hojo clan at Ryuhōji Temple
- Walk along Nanamagari Slope to experience the approach to the castle
- View the main keep ruins from the outside around Seisen Girls’ Academy
- Experience the atmosphere of the castle grounds at Suwa Shrine
- Explore the surrounding ruins and information boards
The tour takes approximately 2-3 hours, allowing you to leisurely explore the historical site.
Points to Note During Your Visit
- The main keep site is located within the grounds of Seisen Girls’ School, so unauthorized entry is prohibited.
- Please be considerate of school events and classes and observe quietly.
- As the ruins are scattered within a residential area, please respect the privacy of residents.
- Some areas, such as Nanamezaka, have slopes and stairs, so comfortable shoes are recommended.
Relationship with the Main Castle Sites of the Later Hojo Clan
Tamanawa Castle occupied an important part of the castle network built by the Later Hojo clan in the Kanto region. The Later Hojo clan, with Odawara Castle as their main base, established branch castles throughout their territory, achieving efficient control of their domain.
Major Castles of the Later Hojo Clan
- Odawara Castle (Odawara City, Kanagawa Prefecture): The main castle of the Later Hojo clan
- Hachioji Castle (Hachioji City, Tokyo): The residence of Hojo Ujiteru, one of the leading mountain castles in the Kanto region
- Hachigata Castle (Yorii Town, Saitama Prefecture): The residence of Hojo Ujikuni, a fortress utilizing the Arakawa River
- Kawagoe Castle (Kawagoe City, Saitama Prefecture): A base for controlling Musashi Province
- Edo Castle (Chiyoda Ward, Tokyo): Built by Ota Dokan, also used by the Later Hojo clan
Tamanawa Castle, working in conjunction with these castles, was an important base responsible for the defense and governance of eastern Sagami Province, the Miura Peninsula, and even the Kamakura area.
Historical Significance of Tamanawa Castle
Role in the Sengoku Period
Tamanawa Castle played an extremely important role in the process by which the Later Hojo clan unified Sagami Province and established hegemony in the Kanto region. It functioned as a forward base to suppress the powerful enemy force, the Miura clan, and later became a base supporting stable governance in eastern Sagami Province.
Known as an “impregnable fortress,” Tamanawa Castle actually repelled attacks by the Miura clan and escaped destruction during the Siege of Odawara. This fact demonstrates the excellence of the castle’s construction techniques and defensive design.
Relationship with Kamakura
Tamanawa Castle was located just a few kilometers north of Kamakura and was an important base for controlling Kamakura. The Later Hojo clan considered Tamanawa Castle important in order to securely control Kamakura, which had been the political, cultural, and religious center since the Middle Ages.
Kamakura still retained many temples, shrines, and the influence of old powers, and it was necessary to place a powerful castle at close range to control them.
Position in Castle History
Tamanawa Castle is considered a fine example of a flatland castle from the Sengoku period that skillfully utilized the terrain in its layout. The design, combining steep terrain with artificial defensive structures, is a valuable example demonstrating the level of castle-building technology at the time.
It is also noteworthy as a castle representing the transitional period from medieval mountain castles to early modern castles. Its history, functioning as a military base during the Sengoku period and then transforming into an administrative jinya (fortified residence) during the Edo period, is crucial for understanding the evolution of Japanese castles.
Preservation and Utilization of Tamanawa Castle Ruins
Designation as a Special Green Space Preservation Area
On June 17, 2003, the Tamanawa Castle Ruins were designated as a Special Green Space Preservation Area. This legally protects the natural environment and historical landscape of the castle ruins, shielding them from uncontrolled development.
The designation as a Special Green Space Preservation Area is an important measure in the increasingly urbanized city of Kamakura to preserve valuable historical heritage and green spaces for future generations.
Local Preservation Activities
In the Tamanawa area, local residents and history enthusiasts are engaged in activities to preserve and utilize the castle ruins. Organizations such as the “Tamanawa Castle Ruins Community Development Council” are at the forefront of these efforts, installing historical site information boards, conducting cleaning activities, and organizing guided tours.
Through these activities, the historical value of Tamanawa Castle has been widely recognized and is being utilized as a local cultural resource.
Future Challenges and Prospects
The following are future challenges for the Tamanawa Castle ruins:
- Detailed Investigation of Remains: Because the main keep site is located within school grounds, full-scale archaeological excavation is difficult. It is desirable to secure opportunities for academic research in the future.
- Improvement of the Visiting Environment: Because the castle ruins are scattered across multiple locations, clear signage and route planning for visitors are needed.
- Dissemination of Historical Information: Compared to the historical importance of Tamanawa Castle, general awareness is still low. More effective information dissemination is necessary.
- Collaboration with Surrounding Historical Sites: Collaboration with other historical sites in Kamakura and castles related to the Later Hojo clan is expected to create a wider-area historical tourism route.
Summary: The Charm of Tamanawa Castle
Tamanawa Castle was a formidable fortress that played a crucial role in the Kanto region during the Sengoku period. It is a historical castle that existed for approximately 280 years, from its construction by Hojo Soun to its Edo period as a fortified residence.
Currently, the main keep site is a school ground, making a complete visit difficult. However, by exploring the remaining ruins and historical sites in the surrounding area, one can imagine the scale and structure of the castle at that time. Related facilities such as Ryuhōji Temple and the Tamanawa History Museum are also abundant, making it an attractive destination for history enthusiasts.
Despite its convenient location within walking distance of Ofuna Station, Tamanawa Castle, which preserves traces of history amidst urbanization, is sure to attract even more attention as a “hidden Sengoku historical site of Kamakura.” Those interested in the history of Sagami Province during the Sengoku period are highly encouraged to visit.
Learning about the history of Tamanawa Castle provides a valuable opportunity to understand the reality of the Later Hojo clan’s rule over the Kanto region and to study the changes in castles during the transition from the Sengoku period to the Edo period. Even from the limited remains, we can imagine the lives of the people of that time and the appearance of this formidable castle, which was said to be impregnable.
