Hiramatsu Castle (Minamiboso City, Chiba Prefecture) Complete Guide | The History and Highlights of the Anzai Clan’s Castle that Welcomed Minamoto no Yoritomo
Located in Ikenouchi, Minamiboso City, Chiba Prefecture, Hiramatsu Castle is known as a crucial historical site that significantly impacted the fate of Minamoto no Yoritomo during the Genpei War. When Yoritomo fled to Awa Province after his defeat at the Battle of Ishibashiyama, the castle’s lord, Anzai Kagemasu, welcomed him, paving the way for the establishment of the Kamakura Shogunate. This article provides a detailed introduction to Hiramatsu Castle, including its historical background, castle structure, existing remains, access methods, and surrounding tourist information.
History of Hiramatsu Castle
Late Heian Period to Early Kamakura Period
The history of Hiramatsu Castle begins with the Anzai clan in the late Heian period. The Anzai clan was a powerful samurai group based in Awa Province, and Hiramatsu Castle was built as their residence.
In August of the 4th year of Jisho (1180), Minamoto no Yoritomo, who had raised an army to overthrow the Taira clan, was defeated by a large Taira army at Ishibashiyama in Sagami Province and fled to Awa Province with only a small retinue. It was at this time that Yoritomo was welcomed by Anzai Kagemasu, the lord of Hiramatsu Castle. Kagemasu provided Yoritomo with food and soldiers, supporting his recovery.
Without this support, Yoritomo’s recovery would have been difficult, and Hiramatsu Castle played a crucial role in the history of the establishment of the Kamakura Shogunate. With Anzai Kagemasu’s support, Yoritomo regained his strength, and in October of the same year, he defeated the Taira army at the Battle of Fujikawa, eventually establishing the Kamakura Shogunate.
Hiramatsu Castle in the Sengoku Period
With the start of the Sengoku period, Awa Province came under the control of the Satomi clan. It is believed that Hiramatsu Castle continued to be used as the residence of the Anzai clan, vassals of the Satomi clan. It is particularly recorded as the site of Anzai Shikibu’s residence and was one of the important bases in the Satomi clan’s rule of Awa Province.
The Satomi clan was a Sengoku period daimyo who ruled the southern part of the Boso Peninsula and engaged in conflicts with the Hojo and Masaki clans. It is presumed that Hiramatsu Castle functioned as a southern base for the Satomi clan’s defense of their territory.
From the Early Modern Period Onward
In the Edo period, Hiramatsu Castle was abandoned. When the Satomi clan was dispossessed of their domain in 1622, Awa Province was divided into shogunate-controlled territories and hatamoto territories, and medieval castles like Hiramatsu Castle ceased to serve their purpose.
Afterward, the castle site became farmland and forest, and after many years, it remains as it is today. From the Showa to the Heisei period, local historians and municipalities conducted surveys, leading to a re-evaluation of Hiramatsu Castle’s historical value.
Structure and Layout of Hiramatsu Castle
Castle Location and Topography
Hiramatsu Castle is a flatland castle built on a hill in the Ikenouchi district of Minamiboso City. Its elevation is approximately 50 meters, overlooking the surrounding rice paddies. The castle’s layout utilizes the tip of a long, narrow hill, showcasing a typical form of medieval castle that skillfully employs natural terrain.
The north and east sides of the castle have steep slopes, while the south and west sides have relatively gentle slopes. This terrain was utilized to construct a structure suitable for defense.
Characteristics of the Main Enclosure (Honmaru)
The main enclosure, the central part of Hiramatsu Castle, is located at the highest point of the hill. The main enclosure is an oval shape, approximately 40 meters east-west and 30 meters north-south, a medium size for a medieval castle.
A stone monument marking the “Hiramatsu Castle Site” currently stands in the main enclosure, allowing visitors to confirm that it is a castle site. This stone monument was erected by Minamiboso City when the site was designated a historical landmark, and it serves as a memorial to the castle’s historical importance.
Traces of earthworks remain around the main enclosure, particularly on the west and south sides, where they are clearly visible. While the earthworks are currently about 1-2 meters high, it is believed they were higher and served a defensive function when the castle was built.
Arrangement of Enclosures
Hiramatsu Castle has a layout of interconnected enclosures, with multiple enclosures arranged around the main enclosure. The second enclosure is located to the west of the main enclosure, at a lower level. It is presumed that the second enclosure functioned as a defensive position to prevent attacks on the main enclosure.
Further west, a flat area, believed to be the third enclosure, continues, forming a tiered defensive structure. These enclosures are designed to gradually prevent enemy incursions, reflecting a typical defensive philosophy of medieval castles.
Moat and Earthworks
Traces of a moat can be seen between the main enclosure and the second enclosure. A moat (horikiri) is a dry moat artificially excavated into a hillside, serving to restrict communication between enclosures and enhance defensive capabilities. While the moats at Hiramatsu Castle are now shallower due to burial and collapse, they are estimated to have been approximately 3-4 meters deep in the past.
Earthworks (dogu) were not only built around the main enclosure but also along the edges of each enclosure, as evidenced by their construction. Fences and walls were built on top of these earthworks, functioning as defensive structures.
Structure of the Entrance (Koguchi)
The entrance (koguchi) of Hiramatsu Castle is believed to have opened on the southwest side of the main enclosure. The entrance (koguchi) served as both an entry point to the castle and the most heavily fortified area. It is possible that the entrance (koguchi) of Hiramatsu Castle had a curved rather than straight structure, suggesting that measures were taken to make enemy intrusion difficult.
Highlights of Hiramatsu Castle
Hiramatsu Castle Site Monument
The “Hiramatsu Castle Site” monument, erected in the main enclosure, is a popular spot for commemorative photos during your visit to the castle ruins. The area around the monument is well-maintained, clearly indicating that it is a castle site. The monument concisely describes the castle’s origins and history, allowing even first-time visitors to understand its importance.
Remains of Earthworks and Moats
The greatest highlight of Hiramatsu Castle is the well-preserved remains of earthworks and moats. The earthworks on the west side of the main enclosure are particularly clear, and their height and shape allow us to imagine the defensive structure of the time. Parts of the moats also remain, making them valuable remains for learning about the structure of medieval castles.
For castle enthusiasts and history buffs, these remains are essential for understanding the military function of Hiramatsu Castle.
View
From the main enclosure, you can enjoy a panoramic view of the surrounding rural landscape. By gazing upon the Awa Province that Anzai Kagemasu may have once seen, you can feel the romance of history. Especially on clear days, you can even see the coastline of the Pacific Ocean in the distance, allowing you to appreciate the geographical importance of the castle’s location.
Natural Environment
The Hiramatsu Castle ruins are currently covered in a mixed forest, allowing you to enjoy nature throughout the seasons. In spring, you can see fresh greenery; in summer, deep green; in autumn, vibrant autumn leaves; and in winter, the remains are clearly visible after the leaves have fallen, each season offering a different appearance.
Access Methods
Access by Public Transportation
To access Hiramatsu Castle by public transportation, the nearest station is JR Uchibo Line “Chikura Station.” From Chikura Station, you can take a local bus or taxi.
- From JR Uchibo Line “Chikura Station”: From the station, take the Tateyama Nitto Bus bound for “Hiradate” or “Awa Shirahama,” and get off at the “Ikenouchi” bus stop. The castle ruins are approximately a 10-minute walk from the bus stop. Since bus services are limited, it is recommended to check the timetable in advance.
- Taxi: Approximately 15 minutes by taxi from Chikura Station, costing around 2,000 yen.
Access by Car
Access by car is the most convenient.
- From Futtsu-Tateyama Expressway “Tomiura IC”: Approximately 30 minutes south on National Route 128, via Prefectural Route 88.
- From Tateyama Expressway “Kimitsu IC”: Approximately 1 hour via National Route 127 and National Route 128.
Parking: There is no dedicated parking lot for the castle ruins, but there are a few parking spaces in nearby vacant lots. When visiting, please be considerate of local residents.
Approach on Foot
To reach the castle ruins, you enter a mountain path from a paved farm road. Since some parts of the mountain path are not well-maintained, comfortable walking shoes are recommended. It takes approximately 5 minutes on foot from the trailhead to the main enclosure.
Important Notes for Visitors
Clothing and Equipment
Since Hiramatsu Castle Ruins is an undeveloped forest area, the following equipment is recommended:
- Shoes: Non-slip, comfortable shoes such as trekking shoes or athletic shoes
- Clothing: Long-sleeved shirt and long pants (to protect yourself from plants and insects)
- Items to Bring: Drinking water, insect repellent spray, hat, towel
Safety Precautions
- There are steep slopes and uneven terrain within the castle ruins. Please be careful not to fall.
- In summer, there are many mosquitoes and bush mosquitoes, so please take thorough insect repellent measures.
- Avoid visiting alone; it is recommended to visit in groups whenever possible.
- It is wise to refrain from visiting during or after rain, as the ground becomes slippery.
Toilets and Rest Facilities
There are no toilets or rest facilities around the castle ruins. It is recommended to use the facilities at Chikura Station or a roadside station before visiting.
Nearby Tourist Attractions
Inamura Castle
Located approximately 8 kilometers northeast of Hiramatsu Castle, Inamura Castle was an important branch castle of the Satomi clan. Inamura Castle also boasts well-preserved medieval castle remains, and visiting it together with Hiramatsu Castle allows for comparative study of medieval castles in Awa Province.
Takita Castle
Located approximately 5 kilometers north of Hiramatsu Castle, Takita Castle is also associated with the Anzai clan. While smaller in scale than Hiramatsu Castle, the remains of earthworks and moats can be seen, providing insight into the appearance of a medieval local lord’s residence.
Tateyama Castle
Located in Tateyama City, adjacent to Minamiboso City, Tateyama Castle is known as the main castle of the Satomi clan. Currently, it is maintained as Shiroyama Park, with a replica keep. At the Tateyama Castle Museum (Hakkenden Museum), you can learn in detail about the history of the Satomi clan and the Sengoku period in Boso.
Visiting Tateyama Castle before or after visiting Hiramatsu Castle will give you a deeper understanding of the Sengoku period history of Awa Province.
Shirahama Castle
Located in Shirahama Town, at the southernmost tip of the Boso Peninsula, Shirahama Castle functioned as a key point for maritime traffic for the Satomi clan. Built on a cliff overlooking the Pacific Ocean, it is known for its magnificent views.
Otaki Castle
Otaki Castle, located in Otaki Town, Isumi District, Chiba Prefecture, is a modern castle where Honda Tadakatsu served as lord. Currently, the keep has been restored, and the Otaki Castle Annex houses exhibits introducing the history of castles in Boso. Comparing medieval castles like Hiramatsu Castle with modern castles like Otaki Castle helps to understand the history of castle development.
Other Castles in Chiba Prefecture
Chiba Prefecture has numerous castle ruins, and visiting them along with Hiramatsu Castle will provide a comprehensive understanding of the history of castles in Boso.
Sakura Castle
Sakura Castle, located in Sakura City, flourished as the residence of a fudai daimyo (hereditary feudal lord) during the Edo period. Currently, it is maintained as Sakura Castle Ruins Park, with well-preserved remains such as earthworks and dry moats. The National Museum of Japanese History is also adjacent, offering opportunities to learn about Japanese history in general.
Hon-Sakura Castle
Spanning Shisui Town and Sakura City, Hon-Sakura Castle is a medieval castle that flourished as the base of the Chiba clan. Large earthworks and dry moats remain, and it is designated as a national historic site. It is one of the most important historical sites in Chiba Prefecture for learning about the structure of medieval castles.
Okamoto Castle
Okamoto Castle, located in Midori Ward, Chiba City, was the residence of a branch of the Chiba clan. Its remains are preserved within a residential area, making it a valuable castle site preserved amidst urbanization.
Honno Castle
Honno Castle, located in Mobara City, is known as the residence of the Toki clan during the Sengoku period (Warring States period). Honno Castle, with its remaining earthworks and moats, is an important historical site for understanding the Sengoku period history of the Boso Peninsula.
Designation of Hiramatsu Castle as a Cultural Property
Hiramatsu Castle is designated as a historical site by Minamiboso City and is protected as an important historical heritage of the region. The city’s board of education installs explanatory signs and performs regular maintenance such as grass cutting.
Further detailed archaeological excavations and academic research are expected to lead to national and prefectural historical site designation.
Castle Stamps and Souvenirs
In recent years, the “castle stamp” boom has spread nationwide, and Hiramatsu Castle also issues its own castle stamps. Castle stamps are popular as souvenirs of castle visits, and the number of collectors is increasing.
Hiramatsu Castle’s castle stamps can be obtained at the Minamiboso City Tourism Association and local tourist facilities. The design incorporates the history of Hiramatsu Castle and the Anzai family crest, making it an ideal souvenir of your visit.
Collecting castle stamps from other castles in Chiba Prefecture, along with those from other castles in Chiba Prefecture, will enhance your enjoyment of touring Chiba’s castles.
The Relationship Between Hiramatsu Castle and Minamoto no Yoritomo
The relationship with Minamoto no Yoritomo is the most important episode when discussing the history of Hiramatsu Castle. In August of the 4th year of Jisho (1180), Yoritomo, defeated at the Battle of Ishibashiyama, fled from Manazuru to Awa Province by ship. It was at this time that Anzai Kagemasu, the lord of Hiramatsu Castle, welcomed Yoritomo.
Kagemasu not only provided Yoritomo with food and soldiers, but also appealed to the samurai of Awa Province for their cooperation. Thanks to this support, Yoritomo was able to quickly regain his strength and gain the support of samurai from Kazusa and Shimosa Provinces.
Yoritomo later established the Kamakura Shogunate, and Anzai Kagemasu was rewarded for his achievements. Kagemasu’s descendants maintained their power in Awa Province throughout the Kamakura period, and Hiramatsu Castle prospered as the base of the Anzai clan.
Thus, Hiramatsu Castle was a crucial turning point in Japanese history, and it has etched its name in history as a key player behind the scenes in the establishment of the Kamakura Shogunate.
Research on Hiramatsu Castle and Future Prospects
Research on Hiramatsu Castle continues by local historians and archaeologists. While previous investigations have revealed some aspects of the castle’s layout and the arrangement of its remains, many aspects remain unclear.
Future archaeological excavations could potentially provide more detailed information about the castle’s age, period of use, and the lifestyle of its lords based on unearthed artifacts. Furthermore, cross-referencing with historical documents is expected to clarify the lineage of the Anzai clan and the historical changes of Hiramatsu Castle.
In Minamiboso City, efforts are underway to utilize castle ruins within the city, including Hiramatsu Castle, as tourist resources. It is hoped that improvements such as enhanced explanatory signs, the development of walking trails, and the implementation of guided tours will increase opportunities for more people to learn about the history of Hiramatsu Castle.
Summary
Hiramatsu Castle, located in Minamiboso City, Chiba Prefecture, played a crucial role in Japanese history as the residence of Anzai Kagemasu, who supported Minamoto no Yoritomo. By welcoming Yoritomo after his defeat at the Battle of Ishibashiyama and providing the foundation for his resurgence, it paved the way for the establishment of the Kamakura Shogunate.
The castle’s remains, including the main enclosure, baileys, earthworks, and moats, are preserved, making it a valuable historical site for studying the structure of medieval castles. It is designated as a historical site by Minamiboso City and protected as an important historical heritage of the region.
While access to Hiramatsu Castle is convenient by car, it is also accessible by public transport. When visiting, please prepare comfortable clothing and equipment and take safety precautions. There are numerous other castle ruins in the surrounding area, such as Inamura Castle, Takita Castle, Tateyama Castle, and Shirahama Castle; visiting these together will provide a deeper understanding of the medieval history of Awa Province.
Chiba Prefecture also has many other castle ruins, including Sakura Castle, Hon-Sakura Castle, and Otaki Castle. Collecting castle stamps while touring the castles of Chiba Prefecture will allow you to experience the rich history and culture of the Boso Peninsula.
Hiramatsu Castle is a place that marked an important turning point in Japanese history and is a historical site worth visiting for history buffs and castle enthusiasts. Why not visit Hiramatsu Castle and reflect on the historical romance of Minamoto no Yoritomo and Anzai Kagemasu?
