The History and Complete Overview of Shiraiwa Castle (Sagae City, Yamagata Prefecture)
Shiraiwa Castle was a Japanese castle located in Shiraiwa, Sagae-sho, Murayama-gun, Dewa Province (present-day Shiraiwa, Sagae City, Yamagata Prefecture). During the Sengoku period, it played a crucial role as a strategic point on the upper reaches of the Sagae River and formed the core of the Shiraiwa Castle complex, consisting of multiple castles built by the Oe clan. This article provides a detailed explanation of Shiraiwa Castle, from its historical background and castle structure to its current state of remains.
Overview of Shiraiwa Castle
Shiraiwa Castle is a medieval mountain castle located in Shiraiwa, Sagae City, Yamagata Prefecture, built on a river terrace on the left bank of the Sagae River. This area was a strategically important transportation hub, connecting the upper reaches of the Sagae River to the Shonai region via Yoshikawa, the site of Oe Hiromoto’s mausoleum, and dividing the upper and lower reaches of the Sagae River alluvial fan.
Shiraiwa Castle was not a standalone fortress, but rather functioned as part of the “Shiraiwa Castle Group,” a complex of castle ruins centered around Inariyama Castle. These castles are believed to have worked in conjunction with each other, forming a defensive system for the region.
Location and Geographical Characteristics
Location: Shiraiwa, Sagae City, Yamagata Prefecture
Shiraiwa is located in the northern part of Sagae City, exhibiting a complex topography of river terraces and tongue-shaped plateaus formed by the Sagae River. The Sagae River, part of the Mogami River system, forms steep valleys in this region, providing natural strongholds and terrain suitable for castle defense.
The surrounding area is surrounded by mountains, with the Ou Mountains to the east, the Dewa Sanzan (including Mount Gassan) to the west, and the Asahi Mountain Range to the north—a mountainous region characteristic of Yamagata Prefecture. This geographical condition was a major factor in making Shiraiwa a strategically important military location.
History of Shiraiwa Castle
Construction and the Rule of the Oe Clan
While there are no clear records regarding the exact construction date of Shiraiwa Castle, it is believed to have been built by the Oe clan, who ruled this area from the Kamakura period to the Nanboku-cho period.
The Oe clan were descendants of Oe Hiromoto, a senior retainer of the Kamakura Shogunate. The lineage of Oe Chikahiro, Hiromoto’s fourth son, acquired territory in Sagae-sho and developed into the Sagae Oe clan. The Shiraiwa Oe clan, who ruled Shiraiwa, was a branch of this Sagae Oe clan and is presumed to have been entrusted with the control of the upper reaches of the Sagae River.
Shiraiwa Castle in the Sengoku Period
During the Sengoku period, the Murayama region of Dewa Province became a battleground for the power struggles of powerful daimyo such as the Mogami, Date, and Uesugi clans. Shiraiwa Castle was no exception and became embroiled in these conflicts.
In particular, in the latter half of the 16th century, the Sagae Oe clan came under pressure from the Mogami clan. In 1584, Mogami Yoshiaki captured Sagae Castle, seizing control of the Sagae Oe clan’s stronghold. While historical records are scarce and details about the role of Shiraiwa Castle and the surrounding castle complex are unclear, it undoubtedly played a part in the Sagae Oe clan’s control.
Changes After the Mogami Clan
After the Sagae Oe clan was destroyed by the Mogami clan, the Shiraiwa area came under Mogami control. When the Mogami clan was dispossessed in 1622, Sagae became a shogunate territory, and Shiraiwa became the domain of Sakai Tadashige.
During this period, amidst the destruction of many medieval castles, Shiraiwa Castle is believed to have lost its military function and been abandoned. From the Edo period onward, the Shiraiwa area developed as an agricultural region, and the former castle remains gradually returned to nature.
Structure of the Shiraiwa Castle Complex
Composition of the Castle Complex
According to the “Yamagata Prefecture Medieval Castle Site Survey Report,” the Shiraiwa Castle Complex is believed to have consisted of multiple castle remains, with Inariyama Castle at its core, as follows:
- Inariyama Castle: The main castle forming the core of the Shiraiwa Castle Complex
- Shiraiwa Hachiman-date: A castle located on the eastern cliff line of Shiraiwa Kamitateyama Mountain
- Other Branch Castles and Forts: Small defensive strongholds strategically placed in the surrounding area
These castles were cleverly positioned utilizing the river terraces and tongue-shaped plateaus of the Sagae River, and built at a distance that allowed for mutual visibility and communication. This type of defense system using multiple castles is a common structure found in mountain castles of the Sengoku period.
Characteristics of Shiraiwa Hachiman-date
Shiraiwa Hachiman-date is a castle within the Shiraiwa Castle Complex for which relatively detailed information remains. Located on the eastern cliff of Shiraiwa Kamitateyama, it is known to have possessed a vast enclosure.
An enclosure (kuruwa) is a flat area within a castle complex, used for garrisoning soldiers, storing supplies, and serving as a command post. The vast size of the enclosure at Shiraiwa Hachimandate indicates that this castle was not merely a lookout or fort, but functioned as a military base of considerable size.
It is presumed that the eastern cliff served as a natural defensive wall, while artificial moats and earthworks were constructed on the south and north sides. However, the area is now covered with bamboo and dwarf bamboo thickets, making detailed confirmation of the remains difficult.
Structural Characteristics as a Mountain Castle
The Shiraiwa Castle complex possesses the typical structure of a mountain castle. Unlike castles on flat land, mountain castles have the following characteristics:
- Utilization of terrain: Maximum use of natural terrain such as river terraces and tongue-shaped plateaus
- Arrangement of baileys: Multiple baileys arranged in a stepped pattern on the mountain slope
- Moat: A moat dug to cut across the ridge, preventing enemy intrusion
- Earthwork: A defensive wall made of piled-up earth surrounding the bailey
- Vertical moat: A moat dug perpendicular to the slope, preventing lateral movement of the enemy
It is believed that these typical mountain castle defensive structures were also present at the Shiraiwa Castle complex, but detailed archaeological excavations have not been conducted, and the full extent of the remains remains unclear.
Successive Lords of Shiraiwa Castle
Regarding the successive lords of Shiraiwa Castle, historical records are limited, making it difficult to trace a detailed genealogy. However, it is certain that the Oe clan ruled this area for generations.
The Lineage of the Oe Clan
The descendants of Oe Chikahiro, the fourth son of Oe Hiromoto, ruled the Sagae Manor and developed as the Sagae Oe clan. The Shiraiwa Oe clan, who ruled Shiraiwa, is believed to have been a branch family of this Sagae Oe clan.
The exact date of the first Shiraiwa Oe clan’s arrival in Shiraiwa is unknown, but it is presumed to be sometime between the late Kamakura period and the Nanboku-cho period. From then until their destruction by the Mogami clan at the end of the Sengoku period, the Shiraiwa Oe clan is thought to have ruled this area for generations.
Shiraiwa under the Rule of the Mogami Clan
After Mogami Yoshiaki destroyed the Sagae Oe clan in 1584 (Tensho 12), Shiraiwa came under the direct rule of the Mogami clan. It is believed that the Mogami clan stationed vassals in Shiraiwa, but specific names of individuals are not recorded in historical documents.
After the Mogami clan’s downfall in 1622, Shiraiwa became part of the territory of Sakai Tadashige and was subsequently incorporated into the system of rule of the early modern daimyo.
Branch Castles and Related Fortresses of Shiraiwa Castle
The Shiraiwa Castle complex functioned as part of the defense system for the upper reaches of the Sagae River. The following related castles existed in the surrounding area:
Sagae Castle
Sagae Castle, the base of the Sagae Ooe clan, was located in the present-day center of Sagae City. Shiraiwa Castle is thought to have served as a branch castle of Sagae Castle, playing a role in the defense of the upper reaches of the Sagae River.
Sagae Castle developed as a flatland castle, and a castle town was formed, but it was captured by Mogami Yoshiaki in 1584, leading to the downfall of the Sagae Ooe clan. After the Mogami clan’s downfall in 1622, Sagae Castle was demolished, and a temporary residence (outpost office) was established on the site.
Other Surrounding Castles
The following castles are presumed to have existed around the Shiraiwa Castle complex:
- Yoshikawa Castle: A castle believed to have existed in Yoshikawa, the site of the ancestral shrine of Ooe Hiromoto.
- Various Forts and Watchtowers: Small defensive strongholds strategically placed along the Sagae River.
These castles cooperated with each other, forming a military network that supported the Sagae Ooe clan’s rule over their territory.
Current Status of Shiraiwa Castle Remains
Current State of Remains
Currently, the Shiraiwa Castle site is covered with forests, bamboo groves, and dwarf bamboo thickets, making it difficult to clearly identify any remains. While traces of baileys, moats, and earthworks may remain as topographical features, detailed surveys and archaeological excavations have not been conducted.
The “Yamagata Prefecture Medieval Castle Site Survey Report” records the location and overview of the Shiraiwa Castle Group, but further investigation is needed to determine the detailed state of the remains.
Cultural Property Designation Status
Currently, the Shiraiwa Castle site is not designated as a national, prefectural, or municipal cultural property. There are numerous medieval castle sites in Yamagata Prefecture, and protecting all of them as cultural properties is difficult.
However, Shiraiwa Castle is an important site for understanding the history of the upper reaches of the Sagae River, and if its historical value is revealed through future investigations and research, there is a possibility of cultural property designation.
History and Culture of Shiraiwa
History of Shiraiwa Village and Shiraiwa Town
The Shiraiwa area developed as an agricultural region throughout the Edo period. With the implementation of the town and village system in the Meiji era, Shiraiwa Village was established, and in 1954 (Showa 29), it became Shiraiwa Town.
Shiraiwa Town belonged to Nishimurayama District, Yamagata Prefecture, and occupied the area on the left bank of the Sagae River. On October 1, 1954 (Showa 29), Shiraiwa Town merged with Sagae Town, Nanbu Village, Daigo Village, Tanizawa Village, Takamatsu Village, and Misumi Village to form Sagae City, which remains to this day.
Cultural Heritage of Shiraiwa
In addition to castle ruins, the Shiraiwa area also contains historical cultural heritage:
Memorial Tower for Thirty-Eight People: This tower commemorates 36 people executed in a peasant uprising in 1638 (Kanei 15), and two people who died after directly appealing to the authorities in Edo, for a total of 38 people. This uprising is a historically important event as a peasant movement in the early Edo period.
Historical Sites Related to Jionji Temple: Around Shiraiwa, there are also historical sites related to Jionji Temple, a representative ancient temple of Yamagata Prefecture.
Access and Visiting Information
Access to Shiraiwa Castle Ruins
Location: Shiraiwa, Sagae City, Yamagata Prefecture
Public Transportation:
- Get off at JR Sagae Station on the JR Aterazawa Line, then take a taxi or bus for approximately 15-20 minutes.
- If using the city bus, take the bus bound for Shiraiwa.
By Car:
- Approximately 15 minutes from Sagae IC on the Yamagata Expressway via National Route 112.
- From the center of Sagae City, take National Route 287 or a prefectural road.
Precautions for Visiting
Shiraiwa Castle Ruins are not a developed tourist area and are covered with forests and bamboo groves. If you wish to visit, please note the following:
- Possibility of Private Property: Much of the castle ruins may be on private property. Avoid unauthorized entry, and if necessary, check with local residents or the Sagae City Board of Education.
- Safety Precautions: As this involves activities in a mountainous forest, appropriate clothing (long sleeves, long pants, hiking boots, etc.) and equipment (map, compass, mobile phone, etc.) are necessary.
- Season: Visiting is difficult during the summer when bamboo and dwarf bamboo thickets are abundant. The period from late autumn to early spring, when the leaves have fallen, is a relatively easy time to visit.
- Avoiding Solo Activities: Solo activities in mountainous forests are dangerous. We recommend traveling in groups.
Nearby Tourist Attractions
The Shiraiwa area and Sagae City have the following tourist attractions:
Shiraiwa Area – One of the Three Difficult Passes of the Mogami River: Known as a rapid section of the Mogami River, it was a difficult place for river transport.
Sagae Hachimangu Shrine: A shrine revered by the Sagae Ooe clan, with historical buildings remaining.
Sagae Onsen (Hot Springs): There are several hot spring facilities in the city where you can relax and unwind after sightseeing.
Cherryland: A tourist facility themed around cherries, where visitors can enjoy local specialties of Sagae City.
Current Status and Challenges of Shiraiwa Castle Research
Limitations of Historical Sources
Historical research on Shiraiwa Castle faces a major challenge: the scarcity of historical sources. Records of medieval regional castles are generally scarce, and detailed records are often lacking, especially for castles of the subsidiary castle class.
While Shiraiwa Castle is mentioned in local history research such as the “Yamagata Prefecture Medieval Castle Site Survey Report” and the “Sagae City History,” many aspects remain unclear, including the construction date, successive lords, and detailed castle structure.
Future Research Possibilities
To clarify the history of Shiraiwa Castle, the following research approaches are possible:
Excavation of Documentary Sources: Descriptions of Shiraiwa Castle may be found in ancient documents of temples and shrines, historical materials related to the Oe clan, and documents of daimyo families such as the Mogami and Date clans.
Archaeological Investigation: Excavation and surveying may reveal the structure, size, and period of use of the castle.
Place Name Research: Distribution surveys of castle-related place names such as “Tate,” “Yate,” “Negoya,” and “Yogai” can estimate the extent of the castle complex.
Comparative Research: Comparative research with other mountain castles of the same period can clarify the characteristics and positioning of Shiraiwa Castle.
Shiraiwa Castle and the Medieval History of Yamagata Prefecture
Positioning of the Murayama Region in the Sengoku Period History
Shiraiwa Castle was one of the stages of power struggles in the Murayama region of Dewa Province during the Sengoku period. This region was characterized by a complex political situation, with local lords such as the Sagae-Oe, Tendo, and Mogami clans vying for power, and further influenced by the Date clan from the south and the Uesugi clan (later the Yonezawa-Uesugi clan) from the north.
Shiraiwa Castle was located at the northernmost edge of the territory controlled by the Sagae Oe clan, and was a strategically important point controlling transportation routes to the Shonai and Mogami regions. The struggle for control of this area is thought to have influenced the balance of power throughout the Murayama region.
History of the Oe Clan and Sagae Manor
Oe Hiromoto was an important official of the Kamakura Shogunate, gaining the trust of Minamoto no Yoritomo and contributing to the establishment of the shogunate’s political structure. His descendants acquired territories in various regions and developed as a samurai family.
The Sagae Oe clan, who ruled Sagae Manor, is said to be descended from Hiromoto’s fourth son, Chikahiro, and ruled this area for approximately 350 years, from the Kamakura period to the Sengoku period. The Shiraiwa Oe clan, as a branch of this Sagae Oe clan, was responsible for controlling the upper reaches of the Sagae River.
In 1584 (Tensho 12), the Sagae Oe clan was destroyed by Mogami Yoshiaki’s capture of Sagae Castle, bringing an end to their long history. This event marked a crucial step in the Mogami clan’s unification of the Murayama region.
Summary
Shiraiwa Castle was a medieval mountain castle located in Shiraiwa, Sagae City, Yamagata Prefecture. During the Sengoku period, it played a vital role as a strategic point in the upper reaches of the Sagae River. Built by the Oe clan, it functioned as part of the Shiraiwa castle complex, centered around Inariyama Castle.
Currently, the castle ruins are covered by forests and bamboo groves, making it difficult to clearly identify any remains. However, it is an important historical site for understanding the history of the Sagae Oe clan and the Sengoku period history of the Murayama region. Further investigation and research are expected to reveal more about the historical value of Shiraiwa Castle.
The Shiraiwa area possesses diverse historical heritage, including not only castle remains but also the 38-person memorial tower that commemorates a peasant uprising during the Edo period. Through these historical sites, one can learn about the rich history and culture of Sagae City.
References
- “Report on the Survey of Medieval Castle Sites in Yamagata Prefecture,” Yamagata Prefectural Board of Education
- “History of Sagae City, Volume 1,” Sagae City
- “Comprehensive Survey of Japanese Castles, Volume 3: Yamagata, Miyagi, Fukushima,” Shin Jinbutsu Oraisha
- Various research papers on the medieval history of the Murayama region
Related Topics
- The Ooe Clan of Sagae
- Ooe Hiromoto
- Mogami Yoshiaki
- Sagae Castle
- Medieval Castles of Yamagata Prefecture
- Sengoku Period History of the Murayama Region
- History of Sagae City
