Masuzawa Castle Ruins (Iwate Prefecture): The Mountain Castle of the Asonuma Clan, Who Ruled Tono, and the History of Masuzawa Hirokatsu’s Rebellion
What are the Masuzawa Castle Ruins?
Masuzawa Castle is a medieval mountain castle site located in Kami-Masuzawa, Miyamori-cho, Tono City, Iwate Prefecture (formerly Miyamori Village). Also known as “Kamimachi Castle” or “Masuzawa Castle,” it is known as the residence of the Masuzawa clan, a branch of the Asonuma clan who ruled the Tono region.
Built on a mountain 260 meters above sea level with a relative height of approximately 110 meters, this mountain castle is located on the mountain behind Chōsenji Temple to the north, and remains such as baileys and dry moats can still be seen today. Among the approximately 13,000 archaeological sites in Iwate Prefecture, it is an important historical site for understanding the ruling system of local powerful families in the medieval period.
Location and Geographical Characteristics
The Masuzawa Castle ruins are located northwest of the center of Tono City, in the mountainous area of Kami-Masuzawa district, Miyamori-cho. This area is near the border of Masuzawa Village and Otomo Village, and held a strategically important position as a transportation hub.
As a mountain castle, its location offers excellent defensive advantages, and it features a unique layout utilizing a ridge extending southeast. The surrounding slopes are steep, resulting in a defensive structure that skillfully utilizes the natural terrain.
History and Background of Masuzawa Castle
Background of Construction and the Asonuma Clan’s Rule of Tono
The exact date of construction of Masuzawa Castle is unknown, but it is estimated to be sometime between the Kamakura and Muromachi periods. The builder is believed to be Asonuma Moritsuna.
The Asonuma clan was originally a samurai family based in Shimotsuke Province (present-day Tochigi Prefecture) and expanded into the Tono region during the Kamakura period. The origins of Masuzawa Castle are traced back to Moritsuna, the second son of Asonuma Mitsutsuna, lord of Yokota Castle in Mutsu Province. He was granted Masuzawa Village and half of Otomo Village, and established a residence (mansion) in Kamimachi. Moritsuna adopted the name Masuzawa Mitsutsuna in this area, becoming the ancestor of the Masuzawa clan.
The Asonuma clan established a strong system of control in the Tono region, deploying family members throughout the area to manage their territory. The Masuzawa clan played a part in this, governing the region from their base at Masuzawa Castle.
Development of the Masuzawa Clan and the Establishment of the Family Temple
In 1574 (Tensho 2), Chōsenji Temple was founded by Masuzawa Hirokatsu. This temple served as the Masuzawa clan’s family temple and still stands at the foot of the Masuzawa Castle ruins. The establishment of Chōsenji Temple is evidence that the Masuzawa clan possessed a certain degree of economic power and influence in the region.
The Masuzawa clan ruled this land for generations, fulfilling their roles as feudal lords by managing agricultural production, collecting taxes, and maintaining local security.
Masuzawa Hirokatsu’s Rebellion and the Nanbu Clan’s Invasion
The most dramatic event in the history of Masuzawa Castle was the rebellion by Masuzawa Hirokatsu.
In 1590, Toyotomi Hideyoshi launched the Odawara campaign, ordering daimyo from across the country to participate. Asonuma Hironaga, the head of the Asonuma clan who ruled Tono, also headed to Odawara, but it is believed that Masuzawa Hirokatsu staged a rebellion during his absence.
While the detailed motives for Hirokatsu’s rebellion are not clearly established by historical records, it is speculated that they may have stemmed from dissatisfaction with the Asonuma main family, a desire for independence, or a secret agreement with the Nanbu clan. This rebellion caused significant disruption to the Asonuma clan’s rule.
The Downfall of the Asonuma Clan and Confiscation of Their Territory
Amidst a series of turmoil, including the rebellion of Masuzawa Hirokatsu, the Asonuma clan gradually lost power. The changing political situation after the Siege of Odawara and the pressure from the powerful Nanbu clan in the north worsened the Asonuma clan’s position.
Ultimately, Asonuma Hironaga was killed in battle against the Nanbu clan, and their territory in Tono was confiscated by the Nanbu clan. As a result, the Masuzawa clan, a branch of the Asonuma clan, also declined, and it is believed that Masuzawa Castle was abandoned.
The exact date of the castle’s abandonment is unknown, but it is estimated to have occurred sometime between the Tensho era (1573-1592) and the Bunroku era (1592-1596).
Nanbu Clan’s Rule of Tono
After the downfall of the Asonuma clan, the Tono region came under the control of the Nanbu clan. The Nanbu family was a daimyo family based in Morioka that ruled a vast territory stretching from northern Iwate Prefecture to eastern Aomori Prefecture.
In Tono, members of the Nanbu family and their retainers were stationed, establishing a new system of rule. The Masuzawa area was also incorporated under Nanbu rule, and Masuzawa Castle disappeared from the historical stage.
Layout and Remains of Masuzawa Castle
Structure as a Mountain Castle
Masuzawa Castle possesses the characteristics of a typical medieval mountain castle. Its location at an altitude of 260 meters, with a relative height of 110 meters from the foot of the mountain, provides sufficient height to defend against enemy attacks.
The castle’s layout has a unique form, utilizing a ridge extending southeast. This arrangement maximizes the use of the terrain, allowing for effective defense even with limited personnel.
Arrangement of Enclosures (Kuruwa)
Multiple enclosures (kuruma) have been identified at Masuzawa Castle. A kuruwa is a flat area within a castle, a space for constructing buildings and stationing soldiers.
The main kuruwa (the central kuruwa equivalent to the honmaru) is surrounded by secondary kuruwa, each demarcated by dry moats and cut slopes (artificial steep slopes). This arrangement of kuruwas indicates that Masuzawa Castle was not merely a residence, but a military facility designed for combat.
Dry Moats and Defensive Structures
The remains of dry moats still exist at the castle site. Dry moats are moats that do not hold water and are important defensive structures for preventing enemy intrusion. The dry moats at Masuzawa Castle demarcated the kuruwa and also served to restrict the movement of attackers.
The surrounding slopes also show artificially cut sections, suggesting they functioned as cut slopes. These defensive structures are valuable remains that demonstrate medieval castle construction techniques.
Current Preservation Status
Although the Masuzawa Castle site is not designated as a historical site, the remains are preserved in relatively good condition. However, since it is a forested area, it is covered with trees and undergrowth, so caution is required when visiting.
It can be accessed via a hiking trail from Chōsenji Temple, but since it is not a well-maintained tourist facility, it is recommended to go with someone experienced in castle ruins or a local guide.
Culture and Traditions of the Masuzawa Region
Masuzawa Kagura
The Masuzawa region has a traditional performing art called “Masuzawa Kagura.” This is designated as an intangible folk cultural property of Tōno City and is a Hayachine-style Kagura that originates from the Ōide Kagura of Tsukimau-machi, Tōno City.
Masuzawa Kagura claims to be of the Shintō-ryū Shinjin-ha school and is said to have been passed down for over 180 years (according to oral tradition). While there is no clear direct connection to the history of Masuzawa Castle, it is an important tradition that demonstrates the cultural continuity of this region.
Chōsenji Temple and the Memories of the Masuzawa Clan
Chōsenji Temple, founded by Masuzawa Hirokatsu, still stands at the foot of the Masuzawa Castle ruins and remains a center of local faith. The temple may hold documents and legends related to the Masuzawa clan, making it an important place for understanding the history of the Masuzawa Castle.
Access and Visiting Information for Masuzawa Castle Ruins
Access Methods
Using Public Transportation:
- Get off at Masuzawa Station on the JR Kamaishi Line, then walk for approximately 20 minutes to Chōsenji Temple.
- From Chōsenji Temple, take the hiking trail to Masuzawa Castle Ruins (approximately 30-40 minutes).
Using a Car:
- Approximately 50 minutes from Hanamaki IC on the Tohoku Expressway via National Route 283.
- Parking is available near Chōsenji Temple (please confirm availability).
Precautions for Visiting
Masuzawa Castle Ruins is not a well-maintained tourist facility, so please note the following points when visiting:
- Clothing and Equipment: Appropriate clothing and shoes for mountain hiking are essential. Be especially careful as it can be slippery after rain.
- Season: Spring to autumn is the best time to visit. Winter is dangerous due to snow.
- Preparation: Bring a map, GPS, and drinking water. Please also check the cell phone signal strength.
- Permission: It is advisable to obtain local permission when passing through private property.
- Safety: Avoid visiting alone; traveling in groups is recommended.
Estimated Time Required
- Visit to Chōsenji Temple: 15-20 minutes
- Hiking to Masuzawa Castle Ruins: 30-40 minutes one way
- Visiting the Castle Ruins: 40-60 minutes
- Total: Approximately 2-3 hours
Other Castle Ruins in Tōno City
When visiting Masuzawa Castle Ruins, visiting other castle ruins related to the Asonuma clan in Tōno City will allow you to understand the history more deeply.
Yokota Castle Ruins
Yokota Castle, the base of the Asonuma clan, is located overlooking the Tōno Basin. As the center of the Asonuma clan’s rule over Tōno, it had a close relationship with Masuzawa Castle.
Ayaori Castle Ruins
This castle, built by a branch of the Asonuma clan, is located in Ayaori-cho, Tono City. Similar to Masuzawa Castle, it formed part of the Asonuma clan’s network of territorial control.
The Importance of Medieval Castle Ruins in Iwate Prefecture
Approximately 13,000 archaeological sites have been identified in Iwate Prefecture, including numerous medieval castle ruins. Among these, the Masuzawa Castle Ruins are a valuable historical site for understanding the governing system of local powerful families and the political situation of the medieval period.
While Iwate Prefecture is known as a treasure trove of Jomon period ruins, it also boasts a wealth of historical heritage from the medieval to early modern periods. From the cultural heritage of Hiraizumi, a World Heritage Site, to the modern Hashino Iron Mine, diverse cultural properties from various eras exist, demonstrating the depth of Japanese history.
Undesignated historical sites like the Masuzawa Castle Ruins are also important cultural heritage sites that convey the history of the region, and their preservation and utilization are highly anticipated.
Current Status and Challenges of Research on the Masuzawa Castle Ruins
Limitations of Historical Sources
Documentary sources concerning the Masuzawa Castle Ruins are limited, leaving many points unclear, such as the construction date, the period of abandonment, and the detailed genealogy of the castle lords. Further research through local historical document surveys and archaeological excavations may reveal new facts.
The Need for Preservation and Utilization
Currently, the Masuzawa Castle Ruins are not designated as a historical site, and no organized preservation activities are underway. While the remains are relatively well-preserved, there is a possibility of future loss due to natural erosion and vegetation encroachment.
Appropriate preservation and utilization strategies, including use in local history education and as a tourist resource, need to be considered.
Contribution to Local History Research
Research on the Masuzawa Castle Ruins contributes to many historical research themes, including the medieval history of the Tono region, the study of the Asonuma clan, and the elucidation of the Nanbu clan’s power expansion process. Continued research by local historians and researchers is expected.
Summary
The Masuzawa Castle Ruins (Tono City, Iwate Prefecture) are a mountain castle built as the residence of the Masuzawa clan, a branch of the Asonuma clan who ruled the Tono region during the medieval period. Located on a mountain 260 meters above sea level with a relative height of 110 meters, the remains of baileys and dry moats still exist today.
The castle was built by Asonuma Moritsuna, and the Masuzawa clan ruled this area for generations. However, during the Tensho era, Masuzawa Hirokatsu rebelled, and subsequently, the Asonuma clan was destroyed in battle against the Nanbu clan, and their territory was confiscated. As a result, Masuzawa Castle was abandoned.
Also known as Kamimachi Castle or Masuzawa Castle, these castle ruins, although not designated as a historical site, are a valuable legacy for understanding the rule system and castle-building techniques of local powerful families during the medieval period. Along with traditional culture such as the Masuzawa Kagura, it conveys the history of the region to the present day.
While hiking gear is necessary for a visit, this historical site is well worth seeing for anyone interested in Tono’s history or castle enthusiasts. As one of Iwate Prefecture’s rich historical assets, its future preservation and utilization are highly anticipated.
