A Complete Guide to the History and Highlights of Asaguchi Castle (Mitoyo City, Kagawa Prefecture) | A Thorough Explanation of the Mock Castle Tower and Remains in Asahiyama Forest Park
What is Asaguchi Castle? | An Overview of Mountain Castles in Sanuki
Asaguchi Castle is a mountain castle built on Mt. Asahi, 238m above sea level, located in Shimoasa, Takase-cho, Mitoyo City, Kagawa Prefecture. Also known as Asahiyama Castle, it functioned as an important base in western Sanuki during the Sengoku period. Currently, it is maintained as Asahiyama Forest Park, with a mock castle tower built on the summit, open to the public as a museum showcasing local history.
A key feature of Asaguchi Castle is its location as a defensive base in western Sanuki Province. Due to its excellent panoramic view of the Mitoyo Plain, it is believed to have served a military surveillance function and, in cooperation with Shiroji Castle, controlled the region. Regarding the castle’s name, there are differing opinions among researchers: some consider Asahiyama Castle and Asaguchi Castle to be the same castle, while others consider them to be separate fortresses.
History of Asaguchi Castle | From Construction to Abandonment
Construction History and Lord
There are no clear records regarding the construction period or builder of Asaguchi Castle, so the details are unknown. However, it is known that Kondo Dewa-no-kami Nagayori resided there as the lord during the Sengoku period. Kondo Nagayori is said to have been the younger brother of Onishi Kakuyo, the lord of Shiroji Castle, suggesting a strong connection between the Onishi and Kondo clans.
The Kondo clan ruled the Asa region as its lords, and Asaguchi Castle is thought to have functioned as an auxiliary castle to Asa Castle (located in Kami-Asa), their residence during peacetime. Asaguchi Castle, a mountain castle, played an important role as a refuge and defensive base during times of emergency.
The Chosokabe Clan’s Invasion and the Escape of Onishi Kakuyo
A crucial turning point in the history of Asaguchi Castle was the invasion of Sanuki Province by Chosokabe Motochika in 1577. Chosokabe Motochika, a Sengoku-era daimyo from Tosa Province, launched an invasion of Sanuki Province with the aim of unifying Shikoku, and captured Shiroji Castle.
Onishi Kakuyo, the lord of Shiroji Castle, lost his home castle to the fierce attack of the Chosokabe army and is believed to have fled to Asaguchi Castle, defended by his younger brother, Kondo Nagayori. This event symbolizes the expansion of the Chosokabe clan’s power in western Sanuki and holds significant meaning in the region’s Sengoku history.
The Castle’s Abandonment and Transition to the Modern Era
There are no clear records of when Asaguchi Castle was abandoned, but it is presumed to have been abandoned after Toyotomi Hideyoshi’s conquest of Shikoku, or due to the “One Castle Per Province” decree in the early Edo period. Afterward, the castle ruins were left neglected as a forest for a long time, but from the late Showa period to the Heisei period, they were developed into Asahiyama Forest Park.
Along with the park development, a replica castle tower was constructed on the mountaintop. This replica tower is not a reconstruction of the historical castle tower, but rather a facility built as a regional symbol, and also serving as an observation deck and museum. Unfortunately, there are allegations that some of the castle’s remains were destroyed during the park development process. Although prior archaeological excavations were conducted, the results of these excavations were not sufficiently made public academically, as mentioned within the museum.
Structure and Layout of Asaguchi Castle
Location and Defensive Functions as a Mountain Castle
Asaguchi Castle is a typical mountain castle built around the summit of Mt. Asahiyama, at an altitude of 238m. Located in the western part of the Sanuki Plain, it boasts an excellent location overlooking the city of Mitoyo and the Seto Inland Sea. This excellent view played a crucial role as a surveillance function for detecting enemy movements early.
The basic structure of this mountain castle is thought to have combined natural defensive capabilities utilizing the steep terrain with artificially constructed defensive facilities. Given its position relative to the surrounding mountains, it is highly probable that a defensive network was formed in conjunction with Shiroji Castle and Asa Castle, making it an important fortress for understanding the control systems of the Sengoku-era daimyo in western Sanuki.
Remains of the Former Site
Records indicate that before the area became the current Asahiyama Forest Park, Asaguchi Castle had typical remains of a mountain castle. According to the exhibits in the museum inside the replica castle tower, the following remains existed:
- Kuruwa: A flat area at the center of the castle, used for buildings and soldier encampments.
- Sekirui: A defensive wall built of stacked stones.
- Dorui: A defensive structure made of piled-up earth.
- Karabori: A moat without water, functioning as an obstacle to prevent enemy intrusion.
Unfortunately, most of these remains were destroyed during the development of Asahiyama Forest Park and the construction of the replica castle tower. Currently, very few clear remains remain, making it difficult to imagine the castle’s appearance in its heyday.
Existing Topography and Traces
Although many remains were lost due to park development, careful observation may reveal traces of the castle. The topography of the mountaintop and the cliff-like terrain along the hiking trails may be remnants of former castle facilities.
Some castle researchers and history enthusiasts are attempting to deduce the former layout of the castle based on old photographs and survey maps from before the park was established.
Highlights of Asahiyama Forest Park
Features and Interior of the Replica Castle Tower
The biggest highlight of Asahiyama Forest Park is the replica castle tower built on the mountaintop. While this tower is not a historical reconstruction but was constructed as a tourist attraction, it is a beloved symbol of the region.
Structure of the Replica Castle Tower:
- 3-story building
- 1st and 2nd floors: Museum with exhibits on local history and Asaguchi Castle
- 3rd floor: Observation deck with 360-degree panoramic views
- Admission: Free
The museum exhibits the history of Asaguchi Castle, materials related to the Kondo and Onishi clans, and the state of the western Sanuki region during the Sengoku period. In particular, it honestly describes how the castle’s remains were lost during park development, making it a thought-provoking exhibit that highlights the importance of cultural property preservation.
View from the Observation Deck
From the observation deck on the third floor of the replica castle tower, you can enjoy a magnificent panoramic view of Mitoyo city. On a clear day, you can even see the Seto Inland Sea and the mountains of Shikoku, allowing you to imagine the former castle lords watching over their territory from this very view.
Main views from the observation deck:
- The vast rural landscape of the Mitoyo Plain
- Mitoyo city
- The Seto Inland Sea (weather permitting)
- The surrounding mountains
This excellent view speaks volumes about why Asaguchi Castle was chosen as a military base.
Ise Asahiyama Hongu Shrine
Asahiyama Mountain is also home to the Ise Asahiyama Hongu Shrine. This shrine is a center of local faith, and the castle ruins and shrine coexist, preserving the history of Asahiyama. The shrine’s history and its relationship to Asaguchi Castle are points of interest during your visit.
The Appeal of a Forest Park
Beyond its aspect as a castle ruin, Asahiyama Forest Park is also developed as a place of relaxation rich in nature. You can enjoy the changing seasons, with cherry blossoms in spring, fresh greenery in early summer, and autumn leaves in fall. It’s a popular walking course for locals, a spot where you can enjoy both history and nature.
The Relationship Between Asaguchi Castle and Asa Castle
Understanding Asaguchi Castle is important because of its relationship with the nearby Asa Castle. Asa Castle is a castle ruin located in Kami-Asa, Takase-cho, Mitoyo City, Kagawa Prefecture, and is a designated historical site of Mitoyo City.
Overview of Asa Castle
Asa Castle was the residence of Kondo Kunihisa, the lord of Asa, during the Sengoku period. It was a mountain castle built on a mountain approximately 160m above sea level, and the remains of earthworks, baileys, and moats are relatively well preserved. Compared to Asaguchi Castle (Asahiyama Castle), Asa Castle’s remains are better preserved, making it a worthwhile historical site for castle enthusiasts. ### Relationship between the Fortress and Residence
Many castles from the medieval to the Sengoku period had a dual structure: a “residence” for peacetime living and a “fortress” for wartime defense. The relationship between Asaguchi Castle and Asa Castle is considered a typical example of this.
- Asa Castle: Peacetime residence, housing administrative functions
- Asaguchi Castle (Asahiyama Castle): Wartime fortress, located in a more defensible location
This structure allowed lords to live in convenient locations during peacetime and retreat to highly defensible mountain castles during wartime, demonstrating flexibility.
Confusion of Names
The names Asaguchi Castle, Asa Castle, and Asahiyama Castle are used interchangeably, and their differing treatment in various sources is a source of confusion.
Main Theories:
- Asaguchi Castle = Asahiyama Castle (theory that they are the same castle)
- Theory that Asaguchi Castle and Asahiyama Castle are separate castles
- Some documents confuse Asa Castle and Asaguchi Castle.
In “The System of Japanese Castles,” Asahiyama Castle and Asaguchi Castle are listed separately. Asahiyama Castle is described as having “remains on the summit of Asahiyama Mountain,” while Asaguchi Castle is described as “the residence of Onishi Samano Nagayori.” However, many modern documents treat Asaguchi Castle and Asahiyama Castle as the same.
Such confusion of names and lack of historical materials are not uncommon in castle research. Understanding these complex circumstances will lead to a deeper understanding when visiting Asaguchi Castle.
Access Information and Visiting Guide
Access by Car
The most convenient way to access Asaguchi Castle Ruins (Asahiyama Forest Park) is by car.
Main Routes:
- Approximately 15 minutes from the Mitoyo-Torisaka Interchange on the Takamatsu Expressway
- Approximately 10 minutes by car from Takase Station on the JR Yosan Line
- Access via Prefectural Road from National Route 11
Asahiyama Forest Park has a parking lot that is free to use. While it’s possible to walk from the parking lot to the replica castle tower, it’s a mountain path, so comfortable walking shoes are recommended.
Access by Public Transportation
If using public transportation, Takase Station on the JR Yosan Line is the nearest station. Taxis are convenient from the station, but since the number of taxis is limited, it’s recommended to check in advance.
Bus services are also limited, making access by car the most practical option.
Points to Note When Visiting
- Opening Hours: The museum in the replica castle tower is usually open from 9:00 to 17:00 (may vary depending on the season).
- Closed Days: Mondays and New Year’s holidays (please check beforehand).
- Admission Fee: Free
- Estimated Time Required: Approximately 1-2 hours
- Attire: Comfortable shoes and clothing are recommended as you will be walking on mountain paths.
- Restrooms: Available within the park.
We recommend checking the tourist information for Mitoyo City and the official information for Asahiyama Forest Park before your visit.
Photo Spot
For castle enthusiasts and photography lovers, the Asaguchi Castle ruins are an attractive photo spot.
Recommended Photo Spots:
- Exterior of the replica castle tower (especially photos with a blue sky as a backdrop look stunning)
- Panoramic view of the Mitoyo Plain from the observation deck
- Distant view of the replica castle tower from the hiking trail
- Collaboration of seasonal flowers and the castle tower
Nearby Tourist Spots and Castles
Nearby Castles
When visiting Asaguchi Castle, exploring the surrounding castles will give you a deeper understanding of the Sengoku period history of western Sanuki.
Asa Castle
- Location: Kami-Asa, Takase-cho, Mitoyo City, Kagawa Prefecture
- Features: Designated historical site of Mitoyo City, relatively well-preserved remains
- An important castle with a close relationship to Asaguchi Castle
Shiroji Castle
- Residence of Onishi Kakuyo
- A historically important castle that was captured by Chosokabe Motochika
- Essential for understanding the history of Asaguchi Castle
Amagiri Castle
- A powerful castle in western Sanuki
- Known as the residence of the Kagawa clan
Tourist Spots in Mitoyo City
- Chichibugahama: A popular beach known as “Japan’s Uyuni Salt Flats”
- Shiunideyama: A scenic spot with cherry blossoms and the Seto Inland Sea
- Hōnenike Dam: A beautiful dam designated as a National Important Cultural Property
The Cultural Value and Challenges of Asaguchi Castle
Lessons from the Loss of Remains
The most regrettable aspect of Asaguchi Castle’s history is the loss of its remains due to park development. This fact is frankly stated in the museum within the replica keep, emphasizing the importance of cultural property preservation.
Although archaeological excavations were conducted, the lack of sufficient academic publication and utilization of the results serves as a crucial lesson for future cultural property preservation. Balancing tourism development and cultural property preservation is a common challenge faced by castle ruins nationwide.
Future Preservation and Utilization
Currently, the Asaguchi Castle site is a popular local attraction known as Asahiyama Forest Park. While most of the remains have been lost, the replica keep fulfills its role in conveying local history.
Future plans include detailed research based on remaining topography and old records, restoration of the castle’s appearance using digital technology, and enhancement of educational programs.
The Significance of Visiting Asaguchi Castle
Asaguchi Castle may be disappointing for castle enthusiasts due to the scarcity of remaining remains. However, this castle ruin is well worth a visit.
Significance of Visiting:
- Learning about the Sengoku period history of western Sanuki: An important stage for understanding the movements of the Kondo, Onishi, and Chosokabe clans.
- Magnificent Views: The spectacular view overlooking the Mitoyo Plain is the same view seen by the former castle lords.
- Considering Cultural Property Preservation: Lessons to be learned from the history of the loss of remains.
- Experiencing Local History: A castle ruin that lives on in the modern age as a park beloved by locals.
Asakuchi Castle is not a castle with perfectly preserved remains, but it is a place that teaches us the importance of considering the value of what has been lost and cherishing local history.
Summary
Asakuchi Castle (Asahiyama Castle) is a Sengoku period mountain castle built on Asahiyama in Mitoyo City, Kagawa Prefecture, and is known as the residence of Kondo Dewa-no-kami Nagayori. It also holds historical significance as the place where Onishi Kakuyo fled after losing Shiroji Castle during the invasion of Chosokabe Motochika.
The site is now developed as Asahiyama Forest Park, and the replica castle tower at the summit is open to the public as a free museum and observation deck. Unfortunately, much of the castle’s remains were lost during the park’s development, but it remains valuable for its magnificent views and as a place to learn about the region’s history.
If you’re interested in the Sengoku period history of western Sanuki, enjoy castle tours, or have the opportunity to visit Mitoyo City, we highly recommend visiting the Asaguchi Castle ruins and reflecting on the history etched into this land.
