A Thorough Explanation of the History and Structure of Naganuma Castle | A Strategic Point in Shinano Province from the Sengoku Period to the Edo Period
##Overview
Naganuma Castle was a flatland castle located in Hobo, Nagano City, Nagano Prefecture, and is known as an important strategic base in Shinano Province. Built on a plain facing the Chikuma River, this castle was the stage for fierce battles between the two major powers, the Uesugi and Takeda clans, during the Sengoku period, and functioned as the administrative center of the Naganuma Domain during the Edo period.
The castle’s location was extremely important both militarily and economically, as it was a crucial transportation hub controlling the Funo ferry crossing on the eastern route of the Hokkoku Kaido road. Built on a fortified site utilizing the Chikuma River as a natural moat, it functioned as an indispensable base for controlling northern Shinano.
There are various theories about the origin of Naganuma Castle, but it is believed to have been built by the Shinano Shimazu clan, who were related to the Satsuma Shimazu clan. This castle existed for over 200 years, from the Sengoku period to the early Edo period, and while its lords changed many times during that time, it left a deep mark on the history of Shinano Province.
History of Naganuma Castle
Construction and Early History
While there are no clear records regarding the construction date of Naganuma Castle, it is believed to have existed since the early Sengoku period. The initial lords were the Shinano Shimazu clan, who were related to the Satsuma Shimazu clan. The Shinano Shimazu clan held considerable power in northern Shinano and controlled the Naganuma area.
In the early Sengoku period, Naganuma Castle was under the influence of the Echigo Uesugi clan (then the Nagao clan). Northern Shinano was a buffer zone between the forces of Echigo and Kai, constantly in a state of tension, and Naganuma Castle was caught in the middle of this turmoil.
During the Takeda Shingen Era
During the Eiroku era (1558-1570), when Takeda Shingen of Kai Province intensified his expansion into northern Shinano Province, the strategic importance of Naganuma Castle increased even further. Takeda Shingen aimed to control northern Shinano, centered around Kawanakajima, and was in fierce conflict with Uesugi Kenshin.
During this period, Shimazu Tadanao, the lord of Naganuma Castle, pledged allegiance to Takeda Shingen, providing Naganuma Castle as an important base for the Takeda clan in northern Shinano.
Takeda Shingen highly valued the strategic importance of Naganuma Castle and ordered Baba Nobuharu (Baba Minonokami Nobuharu), a vassal particularly specialized in castle construction, to carry out a large-scale renovation of the castle. Baba Nobuharu was a renowned general, counted among the Twenty-Four Generals of Takeda, and was also known as a master castle builder. Under his guidance, Naganuma Castle was transformed into a formidable fortress incorporating the Takeda style of castle construction.
As a Takeda Forward Base
After renovations by Baba Nobuharu, Naganuma Castle functioned as a forward base for the Takeda clan in northern Shinano. During the Battle of Kawanakajima, this castle was a crucial base supply for the Takeda army, playing a vital role in supporting the front lines against the Uesugi army.
The geographical location of Naganuma Castle was extremely advantageous for the Takeda clan. Not only could they utilize the Chikuma River as a natural defensive line, but controlling the riverside transportation routes allowed for efficient transport of supplies and movement of troops. Furthermore, controlling a key point on the Hokkoku Kaido road enabled them to monitor the movements of the Uesugi army from the Echigo region and prepare to intercept them if necessary.
Takeda Shingen used Naganuma Castle as his base to strengthen his control over the surrounding region. Powerful Takeda generals were constantly stationed at the castle, overseeing the administration of northern Shinano. During this period, Naganuma Castle is thought to have functioned not only as a military base but also as the administrative center of the Takeda clan’s rule over northern Shinano.
After the Fall of the Takeda Clan
In 1582, when the Takeda clan was destroyed by Oda Nobunaga’s conquest of Kai Province, the entire Shinano Province, including Naganuma Castle, underwent a major transformation. After the fall of the Takeda clan, Shinano Province came under the control of the Oda clan, but with the Honnoji Incident in June of the same year, it entered another period of turmoil.
During this period of turmoil, Uesugi Kagekatsu expanded his power in northern Shinano, and Naganuma Castle also came under the influence of the Uesugi clan. Uesugi Kagekatsu moved south from Echigo, attempting to realize the control of northern Shinano that Uesugi Kenshin had once aimed for. Naganuma Castle once again became an important base for the Uesugi clan in northern Shinano.
Subsequently, during Toyotomi Hideyoshi’s unification of Japan, Uesugi Kagekatsu was recognized as a powerful daimyo under the Toyotomi regime, and northern Shinano, including Naganuma Castle, came under the firm control of the Uesugi clan.
Azuchi-Momoyama Period
In 1590 (Tensho 18), following Toyotomi Hideyoshi’s conquest of Odawara, Uesugi Kagekatsu was transferred to Aizu with a domain of 1.2 million koku. This resulted in a new ruler for Shinano Province.
Most of Shinano Province, including northern Shinano, was divided and ruled by various daimyo of the Toyotomi regime, such as Mori Tadamasa and Tamaru Naomasa. Naganuma Castle also received a new lord during this period, but detailed records are not entirely clear.
In 1598 (Keicho 3), upon the death of Toyotomi Hideyoshi, Japan once again entered an era of turmoil. In the Battle of Sekigahara in 1600, the various daimyo of Shinano Province fought on either the Eastern or Western side. As a result of this battle, Tokugawa Ieyasu seized power and the Edo Shogunate was established.
Edo Period
With the arrival of the Edo period, Naganuma Castle took on a new role. In 1616, Sakuma Katsumune became the first lord of the Naganuma Domain, and Naganuma Castle was developed as the domain’s administrative center. Although the Naganuma Domain was a small domain with a 10,000 koku (unit of rice production) yield, it played an important role in stabilizing the Shogunate’s control in northern Shinano.
The Sakuma clan ruled the Naganuma Domain for three generations, but were dispossessed in 1661, and Hotta Masanaka became the lord in their place. After that, the lords of the Naganuma Domain changed several times, and ultimately, the lineage of Sanada Nobumasa became the lords.
During the Edo period, Naganuma Castle did not become the site of fierce battles like those of the Sengoku period, but it functioned as the center of the domain’s administration and as a base for managing the post town on the Hokkoku Kaido road. The castle town was also developed, and commerce and agriculture flourished.
During the turbulent period at the end of the Edo period, the Naganuma domain was tossed about by the tides of the times, but it survived the Meiji Restoration without suffering major war damage. With the abolition of the feudal domains in 1871, the Naganuma domain was abolished, and Naganuma Castle ceased to serve its purpose.
Structure
The structure of Naganuma Castle strongly retains the characteristics of a flatland castle built on a plain facing the Chikuma River. When it was renovated by Baba Nobuharu during the Sengoku period, the Takeda-style castle-building techniques were introduced, creating a robust defensive system.
Layout and Arrangement
The layout of Naganuma Castle utilized the Chikuma River as a natural moat on the east side. The side facing the river was a steep cliff, making it an extremely difficult terrain for attackers. This topographical advantage was maximized to enhance the castle’s defensive capabilities.
The main keep (Honmaru) was located in the center of the castle, surrounded by the second and third baileys (Ninmaru and Sannomaru). The site of the Honmaru can still be seen today as a topographical elevation, preserving the appearance of the castle’s former central area.
A complex system of moats and earthworks was constructed from the west to the north of the castle. These were designed to prepare for attacks from the plains, and represent a full demonstration of Baba Nobuharu’s castle-building skills.
Earthworks and Moats
The core of Naganuma Castle’s defensive system was the earthworks and moats. Multiple layers of earthworks were built around the castle, with moats positioned between them. These earthworks were not merely for defense, but were strategically placed to restrict enemy movement and give an advantage to firing from within the castle.
Of particular note are the remains of the umadashi (horse enclosure). The current location of Tenno-gu Shrine is believed to be the site of a former umadashi (horse-shaped earthen rampart), with a crescent-shaped moat situated beside it. A umadashi is a characteristic element of the Takeda-style castle construction, a defensive structure positioned in front of the castle gate. Its role was to disperse enemy attacks and prevent direct attacks on the gate.
While it is difficult to know the exact height of the rampart and the depth of the moat today, it undoubtedly possessed sufficient defensive capabilities for a castle of the Sengoku period. The remains below the embankment reveal the high level of castle construction technology of the time.
Structures
A keep (tenshu) was not built at Naganuma Castle. This is a common characteristic of many castles from the Sengoku period, indicating that the castle was built before the architectural style of the keep widespread became. Even after it became the administrative center of the Naganuma Domain during the Edo period, a keep was never constructed.
Various structures, including the Honmaru Goten (main palace), were located within the castle grounds. To fulfill its function as a domain government, it is believed that the castle was equipped with buildings for administrative affairs, the lord’s residence, vassal quarters, and an armory.
According to Edo period records, the castle contained fortified residences and watchtowers. Watchtowers were built at key points within the castle, functioning as bases for surveillance and defense. These structures represent the ingenuity required to construct an effective defensive system within the constraints of a flatland castle.
Regarding stone walls, it that that no large-scale stone walls were constructed at Naganuma Castle. This is likely due to its flatland location and the fact that it was built before the widespread use of stone walls. Instead, earthen ramparts were the primary defensive feature, demonstrating the skillful use of civil engineering techniques appears in its construction.
Water Management System
One of the important features of Naganuma Castle is its water management system utilizing the Chikuma River. The Chikuma River, flowing east of the castle, served not only as a natural moat but also as a source of water for the castle.
It is believed that wells were dug within the castle grounds, a water supply during sieges. One weakness of flatland castles is securing a water source, but Naganuma Castle benefited from the abundant water resources of the Chikuma River, giving it a significant advantage in this regard.
Furthermore, the Chikuma River was also an important transportation route, allowing for the transport of goods via water. This contributed to the castle’s logistical advantages and enabled long-term defense.
Remains
Currently, most of the remains of Naganuma Castle have been lost, but some traces can still be seen. Due to the construction of the Chikuma River embankment and urbanization, it is difficult to imagine the castle’s former appearance, but the topography and some remaining structures offer glimpses into its past.
Existing Remains
The site of the main keep still remains as a topographical elevation, providing clues to the location of the castle’s center. The slightly elevated area compared to the surrounding land indicates the former boundaries of the main keep.
Around Tenno-gu Shrine, traces of the former earthen ramparts of the saddle-shaped outwork are said to remain. This location, below the embankment, is a valuable historical site that conveys the characteristics of the Takeda-style castle construction techniques. While the crescent-shaped moat is not clearly visible today, its existence is inferred from the subtle undulations of the terrain.
Small sections of the earthen ramparts also remain. Although these have been significantly altered by later development, careful observation allows for the estimation of the former defensive line.
Castle Site Monument and Information
A castle site monument for Naganuma Castle stands along the Tsurukawa Road, indicating the former presence of an important castle. The monument serves as an important memorial to the history of Naganuma Castle for future generations.
While detailed information boards are scarce at the site, the Nagano City government has maintained it as a historical site related to the Battle of Kawanakajima, making it a popular destination for history enthusiasts. However, parking and other facilities are limited, so caution is advised when visiting.
Archaeological Excavation and Research
Regarding Naganuma Castle, only limited, full-scale archaeological excavations have been conducted to date. Due to ongoing urbanization, large-scale investigations are difficult. However, research into historical documents and topographical analysis are gradually revealing the castle’s structure and history.
Future development surveys may uncover new remains, and it is hoped that this will further clarify the true nature of Naganuma Castle.
Historical Significance of Naganuma Castle
Naganuma Castle played a crucial role in the Sengoku period history of Shinano Province. Located on the front lines of the conflict between the two major powers, the Uesugi and Takeda clans, it functioned as a base supporting the Battle of Kawanakajima.
The fact that Takeda Shingen ordered Baba Nobuharu to renovate the castle demonstrates its high strategic value. Naganuma Castle was indispensable to the Takeda clan’s management of northern Shinano and was a symbol of their rule.
During the Edo period, it transformed from a Sengoku castle into a modern administrative center, serving as the center of the Naganuma Domain and responsible for governing the region. Although it was a small domain, it played a vital role in the shogunate system as a key base controlling a strategic point on the Hokkoku Kaido road.
While much of the remains have been lost, the history of Naganuma Castle is a mirror reflecting the history of Shinano Province itself. Having witnessed the turning point in Japanese history from the Sengoku period to the Edo period, Naganuma Castle should be carefully preserved and passed down as a regional historical heritage.
Access and Visiting Naganuma Castle
Naganuma Castle ruins are located in Hoho, Nagano City, Nagano Prefecture. If using public transportation, the nearest station is Shinano-Yoshida Station on the Nagano Electric Railway Nagano Line, but it is quite a distance on foot from there, so access by car is more convenient.
It is about a 20-minute drive from the Nagano Interchange on the Joshinetsu Expressway. However, as mentioned above, there is no dedicated parking lot around the castles, so consideration for the surrounding area is necessary when visiting.
While the castle ruins are generally open to visitors, the lack of clearly identifiable remains makes it advisable to study the historical background beforehand. The guide to historical sites related to the Battle of Kawanakajima provided by Nagano City is also a helpful resource.
Numerous other related historical sites, such as the Kawanakajima Battlefield Historical Park, exist in the surrounding area. Visiting these sites together will provide a deeper understanding of the history of northern Shinano during the Sengoku period.
Summary
Naganuma Castle was a fortress that functioned as an important base in northern Shinano Province from the Sengoku period to the Edo period. It was the stage for conflicts between the Uesugi and Takeda clans, and especially after its renovation by Takeda Shingen, it played a crucial role as a forward base for the Takeda clan in northern Shinano.
The castle’s characteristics include its flatland castle structure utilizing the Chikuma River as a natural moat, its defensive system incorporating Takeda-style construction techniques by Baba Nobuharu, and its strategic location on the Hokkoku Kaido road. During the Edo period, it served as the administrative center of the Naganuma Domain, becoming the center of governance during a peaceful era.
Although much of the castle’s structure has been lost, traces of the main keep, earthworks, and a castle monument still allow us to imagine its former glory. The story of Naganuma Castle, an indispensable part of the history of Shinano Province, will undoubtedly continue to be passed down as a valuable historical heritage of the region.
