Hoshigajo Castle (Kagawa Prefecture, Shodo District) Complete Guide | History and Highlights of the Southern Court Mountain Castle on the Highest Peak of the Seto Inland Sea
What is Hoshigajo Castle? | A Fortress in the Sky Overlooking the Seto Inland Sea
Hoshigajo Castle is the remains of a medieval mountain castle located in Shodoshima Town, Shodo District, Kagawa Prefecture. Built on the summit of Mt. Hoshigajo (elevation 816.6m), the highest peak on Shodoshima Island, this castle is known as the highest castle among the islands of the Seto Inland Sea.
Currently protected as a Kagawa Prefecture designated historical site, it attracts attention from history enthusiasts and castle fans as a valuable mountain castle remains from the Nanboku-cho period. Mt. Hoshigajo consists of two peaks: the west peak (elevation 804.9m) and the east peak (elevation 816.6m). The west peak functioned as the main castle, and the east peak as the fortified castle.
From the mountaintop, you can enjoy a panoramic view of Harima Nada and the Seto Inland Sea, and on clear days, you can even see as far as Shikoku and the Chugoku region—a truly spectacular viewpoint. While it was a strategically important location in the Middle Ages, it is now a popular scenic spot attracting many tourists.
History of Hoshigajo Castle | The Turmoil of the Northern and Southern Courts and Sasaki Nobutane
Background of the Castle’s Construction and the Northern and Southern Courts Period
The exact date of Hoshigajo Castle’s construction is unknown, but it is believed to have been built in 1339 (En’en 4 / Ryakuō 2) by Sasaki Saburozaemon-no-jo Nobutane, or Akura Nobutane, a powerful local lord of Bizen Province (present-day Okayama Prefecture).
The Northern and Southern Courts period was a turbulent era of conflict between the Southern Court, centered on Emperor Go-Daigo, and the Northern Court, supported by Ashikaga Takauji. The Seto Inland Sea was a crucial maritime trade route for both sides, and fierce battles were fought for control of it.
Sasaki Nobutane’s Uprising and Control of Shodoshima
Sasaki Nobutane, a general of the Southern Court, raised an army on Shodoshima in 1339. As a powerful local lord of Kojima, Nobutane played a vital role in the Southern Court’s strategy of controlling the Seto Inland Sea.
Nobutane established Hoshigajo Castle as his central base, bringing the entire island under his control and employing a strategy of fortifying the island. Shodoshima, located in the central part of the Seto Inland Sea, possessed a geographical advantage overlooking the Harima Sea and the Bisan Strait, making it an ideal location for monitoring and controlling maritime traffic.
The Battle with the Northern Court and the Fate of the Castle
The activities of the Southern Court, based at Hoshigajo Castle, posed a significant threat to the Northern Court. During the Shohei era (1346-1370), forces led by Hosokawa Moroji, a supporter of the Northern Court, launched an attack on Shodoshima Island.
Hosokawa Moroji was a powerful daimyo (feudal lord) of the Muromachi Shogunate and a central figure for the Northern Court in the Shikoku region. Hoshigajo Castle was a strong defensive structure utilizing the natural terrain, but it is believed to have ultimately fallen to the Northern Court’s attack.
While there are no clear records of how Hoshigajo Castle was used afterward, it is presumed that its military role ended with the cessation of the Nanboku-cho period (Northern and Southern Courts period).
Structure and Remains of Hoshigajo Castle | A Mountain Castle Utilizing Natural Fortifications
Layout Utilizing the Terrain
Hoshigajo Castle is built on Hoshigajo Mountain, a mountain with such rugged terrain that it is also called “Kensozan” (a steep, treacherous mountain). The most distinctive feature of this mountain castle is its direct utilization of natural cliffs and steep terrain as defensive structures. The castle has a double-enclosure structure utilizing two peaks, the western and eastern peaks. The western peak served as the main castle, and the eastern peak as a defensive outpost. A saddle exists between the two peaks, and it is believed that defensive structures were also built there.
The mountaintop is surrounded by large cliffs, making it a natural stronghold that was extremely difficult for attackers to approach. This topographical advantage is the reason why even a small number of defending forces could withstand a long siege.
Main Remains That Can Be Confirmed
Currently, the following remains can be confirmed at the Hoshigajo Castle site:
Enclosures (Kuruwa): Several flat areas remain on the mountaintop, which are thought to be the remains of enclosures used as soldier garrisons or command posts. Major enclosures were located on both the western and eastern peaks.
Stone Wall Remains: Traces of stacked stones can be seen in various places. These may have been defensive walls or building foundations. A notable feature of this medieval mountain castle is the relatively solid stonework that can be observed.
Moat (Horikiri): Traces of a moat dug to cut across the ridge remain. This was an important defensive structure to prevent enemy intrusion.
Earthwork (Dorui): Traces of earthworks, piled up with earth, can be seen around some of the baileys.
Characteristics as a Medieval Mountain Castle
Hoshigajo Castle possesses the typical characteristics of a medieval mountain castle. Unlike early modern castles that made extensive use of stone walls, it is characterized by a structure that skillfully combines the terrain with natural materials such as wood, earth, and stone.
Its location overlooking the Seto Inland Sea was ideal not only for military surveillance but also as a base for controlling maritime traffic. On clear days, ships navigating the Harima Sea and the Bisan Seto Strait could be seen in the distance, allowing for constant monitoring of maritime activity.
Furthermore, near the summit, there are stone structures resembling Buddhist pagodas, suggesting that the site may have served not only as a castle but also as a place of worship.
Natural Environment of Hoshigajo Mountain and Surrounding Attractions
Spectacular Views from the Highest Peak of the Seto Inland Sea
Hoshigajo Mountain, at an elevation of 816.6m, is the highest mountain among the islands floating in the Seto Inland Sea. The view from the summit is breathtaking, offering a 360-degree panoramic vista.
To the north lies the Harima Sea, and on clear days, you can see as far as the Kojima Peninsula in Okayama Prefecture and Himeji. To the south are the townscape of Shodoshima Island, the Seto Inland Sea, and even the mountains of Shikoku. To the east and west, the islands scattered across the Seto Inland Sea float, making this a truly spectacular viewpoint overlooking the sea from the heart of the Seto Inland Sea.
The scenery, especially at sunset, is beautiful. The view of the setting sun over the Seto Inland Sea and the silhouettes of the islands captivates visitors.
Location relative to Kankakei Gorge
To the west of Hoshigajo Mountain lies Kankakei Gorge, one of Japan’s three most beautiful gorges. Kankakei Gorge is a representative scenic spot on Shodoshima Island, known for its beautiful gorge with its series of strangely shaped rocks and boulders.
Kankakei Gorge is also known as “Mikasayama” and is geographically close to Hoshigajo Mountain. While many tourists visiting Shodoshima Island visit Kankakei Gorge, relatively few venture to the Hoshigajo Castle ruins, making it a hidden gem where you can quietly enjoy historical exploration.
Rich Natural Environment
The area around Hoshigajo Mountain is blessed with abundant nature. Seasonal plants can be seen along the hiking trails, and the scenery is particularly beautiful during the fresh greenery of spring and the vibrant autumn foliage.
The area near the summit is windy, resulting in unique vegetation. Furthermore, the unique environment, a blend of the warm climate characteristic of the Seto Inland Sea and the climate of mountainous regions, provides a diverse habitat for various organisms.
Access and Hiking Information
Main Access Routes to Hoshigajo Mountain
To visit the Hoshigajo Castle ruins, you need to hike Hoshigajo Mountain. The main hiking routes are as follows:
Kankakei Ropeway Route: This is the most common access method. A hiking trail is maintained from the Kankakei Ropeway’s summit station, making it a relatively easy route. It takes approximately 2-3 hours to walk from the summit station to the summit of Hoshigajo Mountain.
Kamikakeyama Route: There is also a route that ascends directly from the center of Shodoshima Island. This is a more serious hike and requires more physical strength and time.
Access to Shodoshima Island
Shodoshima Island is accessible by ferry from Honshu or Shikoku:
- Access from Okayama Prefecture: Ferries operate from Hinase Port and Shin-Okayama Port in Okayama Prefecture to Tonosho Port or Sakate Port on Shodoshima Island.
- Access from Kagawa Prefecture: Ferries operate from Takamatsu Port to Tonosho Port or Ikeda Port.
- Access from Hyogo Prefecture: Ferries operate from Himeji Port to Fukuda Port.
After arriving on Shodoshima Island, it is convenient to head towards Kankakei Gorge by rental car or local bus.
Precautions for Hiking
When hiking Mt. Hoshigajo, please note the following:
- Clothing and Equipment: As it is a mountainous area with an altitude of over 800m, appropriate clothing and shoes for hiking are necessary. Windproof clothing is especially important near the summit due to strong winds.
- Water and Food: There are no shops near the summit, so bring plenty of water and snacks. – Weather Check: Even though it’s an island in the Seto Inland Sea, the weather at the summit can change quickly, so checking the weather forecast beforehand is important.
- Time Allocation: Plan your itinerary with plenty of time to descend before sunset.
- Caution for Solo Hiking: If possible, hiking with others is preferable. If hiking alone, consider submitting a hiking plan.
Nearby Tourist Spots and the Charms of Shodoshima
Kankakei Gorge
Located on the west side of Hoshigajo Mountain, Kankakei Gorge is a representative scenic spot of Shodoshima. Formed by volcanic activity approximately 13 million years ago, its unique landscape of strangely shaped rocks and boulders is its charm. You can enjoy the beauty of the gorge while taking an aerial stroll on the ropeway.
Angel Road (Angel’s Walkway)
This sandy path near Tonosho Port only appears at low tide. Known as a sacred place for lovers, there’s a legend that wishes will come true if you cross it hand in hand.
Shodoshima Olive Park
This facility symbolizes Shodoshima, the birthplace of olive cultivation in Japan. Olive groves spread across the hillside, with photo opportunities such as a Greek-style windmill scattered throughout.
Hishio no Sato (Soy Sauce Village)
Shodoshima is also famous as a production area for soy sauce and tsukudani (simmered seafood and vegetables). The Hishio no Sato area features historic soy sauce breweries, offering tours and gourmet treats such as soy sauce soft serve ice cream.
Twenty-Four Eyes Film Village
This facility recreates the filming locations of the movie “Twenty-Four Eyes,” a novel by Sakae Tsuboi. A primary school and a fisherman’s house from the early Showa period have been recreated, allowing visitors to enjoy a nostalgic atmosphere.
The Cultural Value of Hoshigajo Castle
Protection as a Prefectural Designated Historic Site
Hoshigajo Castle ruins are protected under the Cultural Properties Protection Law as a Kagawa Prefecture designated historic site. As a mountain castle ruin from the Nanboku-cho period, it is considered a valuable historical site for understanding the castle construction techniques and strategies of the time.
As a typical example of a medieval mountain castle in the Seto Inland Sea region, and as a historical site that tells the story of the struggle for control of the Seto Inland Sea during the turbulent Nanboku-cho period, it holds high academic value.
Significance as a Regional Historical Heritage Site
Shodoshima Town has positioned the Hoshigajo Castle ruins as an important regional historical heritage site and is working to preserve and utilize it. Regular mowing and maintenance of the remains are carried out, creating an environment where visitors can safely view the site.
Research by local historians and history enthusiasts continues, accumulating new discoveries and knowledge.
Best Season for Visiting and Event Information
Charms of Each Season
Spring (March-May): The fresh greenery is beautiful, making it the perfect season for hiking. The temperature is mild, and the view from the mountaintop unfolds softly through the spring haze.
Summer (June-August): This is the season when the blue sea of the Seto Inland Sea looks its most beautiful, but the temperature is high, and caution against heatstroke is necessary. Early morning hiking is recommended. Autumn (September-November): The autumn foliage season offers beautiful scenery as the entire mountain is ablaze with color. The air is often clear, allowing for expansive views and ideal photography.
Winter (December-February): Fewer visitors allow for a peaceful historical exploration. The air is exceptionally clear, offering the most expansive views of the year from the mountaintop. However, warm clothing is essential.
Main Events on Shodoshima Island
Shodoshima Island hosts a variety of events throughout the year. In conjunction with a visit to Hoshigajo Castle, we also recommend visiting during these event periods:
- Shodoshima Olive Blossom Season (Late May to Early June): Various events timed to coincide with the olive blossom season.
- Setouchi Triennale (Held Every 3 Years): A contemporary art festival where Shodoshima is one of the venues.
- Shodoshima Festival (October): An autumn festival where you can enjoy local traditional events and specialty products.
Points of Interest for Castle Enthusiasts
Highlights and Observation Points of the Ruins
Here are some points that castle enthusiasts should pay attention to when visiting Hoshigajo Castle:
Arrangement of Enclosures on the West Peak (Main Castle): By observing the arrangement of the main enclosure and surrounding enclosures, you can understand the layout of a medieval mountain castle. The arrangement of enclosures along the terrain demonstrates a design philosophy that makes maximum use of the natural topography.
Defensive Structure of the East Peak (Final Castle): You can confirm the structure of the final defensive stronghold. Its defensive design is characterized by its use of the rugged terrain.
Observation of Stone Masonry Remains: Relatively solid stone masonry remains for a medieval mountain castle, providing clues to the castle-building techniques of the time.
View and Strategic Location: By actually overlooking the Seto Inland Sea from the mountaintop, you can experience the strategic value of this castle.
Comparison with Other Seto Inland Sea Castles
While many medieval mountain castles exist in the Seto Inland Sea region, Hoshigajo Castle is distinctive in the following respects:
- High Elevation: A castle built on the highest peak in the Seto Inland Sea islands.
- Remains from the Nanboku-cho Period: Valuable as a castle clearly linked to the history of the Nanboku-cho period.
- Maritime Traffic Monitoring Function: Clear location aimed at controlling the Seto Inland Sea.
Latest Trends in Hoshigajo Castle Research
Archaeological Surveys and New Discoveries
Recent surveys are accumulating new knowledge about Hoshigajo Castle. Local education boards and researchers are continuously conducting surveys and documentary research, deepening our understanding of the castle’s structure and historical background.
In particular, detailed analysis of the layout of the baileys and stone wall remains is revealing traces of construction techniques and renovations. Analysis of excavated artifacts is also providing clues about the realities of life and battles within the castle.
Record Preservation Using Digital Technology
Record preservation of the remains using modern technology is also progressing. Detailed records of the remains are being created using drone aerial photography and 3D scanning technology, which will be used for future research and preservation activities.
Summary | Experience the Charm of Hoshigajo Castle
Hoshigajo Castle is a rare historical site where you can enjoy the historical romance of the Nanboku-cho period and the spectacular views of the Seto Inland Sea simultaneously. This mountain castle, built by Sasaki Nobutane as a base for the Southern Court, still maintains its imposing presence as a natural fortress even after more than 600 years.
The panoramic view of the Seto Inland Sea from the 816.6m-high summit evokes images of the historical events that once unfolded here. This is a precious place where you can experience the strategic importance of the Seto Inland Sea during the turbulent Nanboku-cho period, while viewing the remains of a medieval mountain castle up close.
When visiting Shodoshima Island, in addition to popular tourist spots like Kankakei Gorge and Angel Road, be sure to extend your trip to Hoshigajo Castle Ruins. The historical value and breathtaking views that await you more than compensate for the effort of the climb.
For history buffs, castle enthusiasts, and anyone seeking beautiful scenery, Hoshigajo Castle is a special place well worth visiting.
