A Thorough Explanation of Komakiyama Castle’s History and Highlights | An Innovative Castle Built by Oda Nobunaga
What is Komakiyama Castle?
Komakiyama Castle is a flatland castle built on an isolated mountain at an elevation of 85.9 meters in the central part of Komaki City, Aichi Prefecture. Known as the first full-fledged castle built by Oda Nobunaga himself during the Sengoku period, it occupies an important position in the history of Japanese castles. The entire Komakiyama mountain, approximately 600 meters east-west and 400 meters north-south, was used as a castle facility, and the entire mountain is now a nationally designated historical site.
Komakiyama, standing isolated in the Nobi Plain, has the Gose River to the east and the Sakai River to the west, with these rivers functioning as natural moats. Located approximately 12 kilometers from Inabayama Castle (later Gifu Castle), it was a strategically important location as a base for the conquest of Mino Province.
The History of Oda Nobunaga’s Construction of Komakiyama Castle
Relocation from Kiyosu to Komakiyama
In 1563 (Eiroku 6), Oda Nobunaga moved his residence from Kiyosu Castle to Komakiyama and began the construction of a full-fledged castle. This relocation had a clear strategic intention. At the time, Nobunaga was engaged in ongoing warfare with the Saito clan of Mino Province, and Kiyosu Castle was geographically disadvantageous as a base for conquering Mino.
Komakiyama was close to Mino and was ideally located as a forward base for conquering Inabayama Castle. By building a castle in this location, Nobunaga sought to establish a headquarters for his Mino campaign.
Innovative Use of Stone Walls
The most distinctive feature of Komakiyama Castle was the construction of stone walls in the main enclosure at the mountaintop. During the Sengoku period, castle defenses were generally based on moats and earthworks. However, Nobunaga adopted full-scale stone walls at Komakiyama Castle.
Recent archaeological excavations by the Komaki City Board of Education have revealed numerous stone walls around the mountaintop. These walls were constructed using a technique called “nozurazumi,” where natural stones are stacked as they are, and represent a precursor to the stone wall techniques used in later castles such as Azuchi Castle and Osaka Castle.
The stone walls of the main enclosure reach several meters in height and were a crucial structure supporting the buildings on the mountaintop. The existence of these stone walls indicates that Komakiyama Castle was not merely a temporary fort, but was planned as a full-fledged residence.
Development of the Castle Town
At the same time as building Komakiyama Castle, Nobunaga developed a castle town on the south side of the mountain. This castle town holds significant historical importance as the first town to implement the new urban policies of the Oda-Toyotomi regime (the period when Oda Nobunaga and Toyotomi Hideyoshi held power).
In the castle town, policies were implemented to attract merchants and artisans and stimulate economic activity. Roads were laid out in a grid pattern, demonstrating a planned urban design. This method of developing the castle town became the prototype for the later castle towns of Azuchi and Osaka, and had a significant influence on the development of early modern castle towns.
A mere four years during Nobunaga’s era
Nobunaga resided at Komakiyama Castle for only four years, from 1563 to 1567. In 1567, Nobunaga succeeded in capturing Inabayama Castle, a long-held ambition, and renamed it Gifu Castle, moving his base of operations there.
For Nobunaga, having achieved his goal of conquering Mino Province, Komakiyama Castle had fulfilled its purpose. After Nobunaga moved to Gifu Castle, Komakiyama Castle was abandoned, and its fortifications gradually fell into disrepair.
The Battle of Komaki and Nagakute and Komakiyama Castle
Reuse as a Camp Fortress by Tokugawa Ieyasu
Komakiyama Castle reappeared on the historical stage during the Battle of Komaki and Nagakute in 1584. In this battle, where Toyotomi Hideyoshi faced the combined forces of Oda Nobuo and Tokugawa Ieyasu, Ieyasu established his headquarters on Komakiyama.
Ieyasu utilized the remains of Komakiyama Castle, built by Nobunaga, and redeveloped it as a camp fortress. He strengthened its defenses by constructing new earthworks, moats, and baileys not only on the mountaintop but also on the slopes and foothills.
Confrontation with Hideyoshi’s Army
In the Battle of Komaki and Nagakute, Komakiyama Castle played a crucial role as a base for Ieyasu’s army. Hideyoshi’s army, based at Inuyama Castle, was positioned north of Komakiyama. The two armies faced each other for approximately two months, centered around Komakiyama, resulting in a tense situation. Ieyasu utilized the strategic advantages of Mount Komaki to wage a battle on equal or even superior terms against Hideyoshi’s large army. Although the conflict ultimately ended through a political truce, Komakiyama Castle served as a stage for demonstrating Ieyasu’s military talent.
Remains from the Ieyasu Era
Many remains from the Battle of Komaki-Nagakute still exist on present-day Mount Komaki. The group of baileys, earthworks, and dry moats on the mountainside are thought to have been constructed during this period. The layered existence of remains from both the Nobunaga and Ieyasu eras is a major characteristic of Komakiyama Castle.
Structure and Layout of Komakiyama Castle
A Castle Composed of Six Districts
Recent research on the castle’s layout has revealed that, at the time of its construction, Komakiyama Castle encompassed the entire mountain and was composed of six districts.
Centered around the main bailey at the summit, multiple baileys were arranged on the mountainside, and defensive structures were also deployed at the foot of the mountain. This method of fortifying the entire mountain was groundbreaking for its time, demonstrating Nobunaga’s advanced castle-building skills.
Structure of the Main Enclosure
The main enclosure at the mountaintop is a flat area surrounded by stone walls, and the remains of a building foundation have been confirmed. Excavations have unearthed foundation stones indicating the existence of a large building, as well as artifacts such as roof tiles.
From the main enclosure, one can see a panoramic view of the Nobi Plain, making it a strategically and symbolically important space. Based on the height of the stone walls and the scale of the building, it has been suggested that a structure equivalent to a keep (tenshu) may have existed here.
Main Approach and Ascent Route
The main approach to Komakiyama Castle, the Otemichi (main approach road), was built from the south side of the mountain towards the summit. In 2024, the Otemichi was renovated, allowing visitors to see it in a state close to its original appearance.
Along the Otemichi, defensive enclosures and entrances (koguchi) are strategically placed, demonstrating various measures to prevent enemy intrusion. By following the ascent route, one can experience the castle’s defensive system from the Sengoku period. ### Moats and Earthworks
Komakiyama Castle had numerous moats and earthworks on its slopes and foothills. These are a mixture of remains from both the Nobunaga and Ieyasu periods, and their full extent is gradually being revealed through archaeological excavations.
Remains of moats and wells have been discovered at the eastern foothills, and are thought to have functioned as boundary structures separating the castle town from the castle grounds. The earthworks were built to surround the baileys, enhancing their defensive capabilities.
Remains of Komakiyama Castle and Results of Archaeological Excavations
Discovery of Stone Walls
Previously, Komakiyama Castle was thought to be a temporary fort for the invasion of Mino Province, as Nobunaga only resided there for four years. However, this perception has changed dramatically thanks to continuous archaeological excavations by the Komaki City Board of Education.
The discovery of numerous stone walls in the main bailey area proved that Komakiyama Castle was a full-fledged residence. Stone walls have been discovered not only on the mountaintop but also in multiple locations on the mountainside, indicating that stone walls were used over a wide area.
Foundation Stones of Buildings
During the excavation of the mountaintop, numerous foundation stones of large buildings were discovered. The arrangement of these foundation stones revealed that multiple buildings were systematically positioned.
Based on the size and arrangement of the buildings, it is believed that the main enclosure contained not only residential facilities but also buildings functioning as administrative offices. Nobunaga likely conducted his affairs here and planned his strategy for conquering Mino Province.
Excavated Artifacts
The excavation unearthed a variety of artifacts, including roof tiles, ceramics, and metal products. The discovery of roof tiles is particularly significant, indicating the existence of tiled-roof buildings at Komakiyama Castle.
During the Sengoku period, tiled-roof buildings were limited to high-status structures. The use of roof tiles at Komakiyama Castle suggests that this castle was an important base for Nobunaga.
Well-Preserved Ruins
One reason why the ruins of Komakiyama Castle are so well-preserved is that no large-scale development took place after the castle was abandoned. From the Edo period onward, Komakiyama was essentially preserved as a forest and remained largely unchanged until modern times.
As a result, the ruins from the Nobunaga and Ieyasu eras are well-preserved underground, and modern archaeological excavations are gradually revealing their full extent.
Current Komakiyama Castle and Historical Park
Development as a Historical Park
Currently, the entire Komakiyama area has been developed as a historical park, serving as a place of relaxation for citizens. In spring, it’s a popular spot for cherry blossoms, allowing visitors to enjoy both history and nature.
Walking trails are maintained within the park, making it easy to climb to the summit. Information boards explaining the ruins are installed along the trails, allowing visitors to enjoy a stroll while learning about history.
Komakiyama History Museum (Komaki Castle)
At the summit of the mountain stands the Komakiyama History Museum, a castle-like building constructed in 1967. While not a historically accurate reconstruction, it is a beloved symbol and landmark of Komaki City.
The museum’s interior is a well-maintained museum displaying the history of Komakiyama Castle and excavated artifacts. From the top floor, you can enjoy a panoramic view of the Nobi Plain, allowing you to imagine the scenery seen by figures like Nobunaga and Ieyasu.
Rekishiru Komaki (Komakiyama Castle Historical Site Information Center)
At the foot of Mount Komaki is the Rekishiru Komaki (Komakiyama Castle Historical Site Information Center), which opened in 2017. This facility presents the history of Komakiyama Castle in an easy-to-understand manner, based on the latest archaeological excavation findings.
Inside the museum, exhibits using CG and dioramas allow visitors to visually understand the appearance of Komakiyama Castle in its heyday. The museum also displays actual artifacts unearthed during archaeological excavations, allowing visitors to experience the spirit of the Sengoku period.
Admission is free, making it a must-see facility when visiting Komakiyama Castle.
Historical Significance of Komakiyama Castle
Roots of Early Modern Castles
Komakiyama Castle occupies an extremely important position in the history of Japanese castles. As a castle that made full use of stone walls, it became the root of later early modern castles such as Azuchi Castle, Osaka Castle, and Edo Castle.
The stone wall techniques and layout methods that Nobunaga experimented with at Komakiyama Castle had a significant influence on subsequent castle architecture. Komakiyama Castle is an important example of the transitional period from medieval mountain castles to early modern flatland castles and hill castles.
Pioneer of Castle Town Policy
The Komakiyama castle town is important as a pioneer of urban policy under the Oda-Toyotomi regime. Features common to later castle towns, such as planned street layouts and policies for the concentration of merchants and artisans, can already be seen. Nobunaga learned urban management techniques here and further developed them in the later Azuchi Castle town. His economic policies, such as the Rakuichi-rakuza (free market), may also have been based on his experiences in Komaki.
Nobunaga’s First Step Towards Unifying Japan
The construction of Komakiyama Castle was a crucial first step in Nobunaga’s path to unifying Japan. By building Komakiyama Castle as a base for conquering Mino Province and using it as his headquarters to conquer Inabayama Castle, Nobunaga gained a foothold for expansion into the Tokai and Kinai regions.
The four years at Komakiyama Castle were a crucial period for Nobunaga, marking the beginning of his journey to becoming the ruler of Japan.
Access and Visiting Information for Komakiyama Castle
Access Method
Komakiyama Castle can be accessed in approximately 20 minutes on foot from Meitetsu Komaki Line “Komaki Station,” or approximately 5 minutes on foot from the Komaki City Community Bus “Komaki City Hall” bus stop. For those traveling by car, the Komakiyama North Parking Lot (free) is available.
Located approximately 1.7 kilometers west of Komaki Station, Komakiyama Castle is easily accessible from the city center.
Points to Note When visiting Komakiyama Castle, we recommend keeping the following points in mind:
- Gain background knowledge at Rekishiru Komaki
- Climb the Ote-michi (main approach road) and experience the castle’s route in its heyday
- Observe the remains of earthworks and moats at the Yamagawa no Kuruwa (mountainside enclosures)
- View the stone walls at the Summit Main Enclosure
- Visit the Komakiyama History Museum to see the exhibits and enjoy the view from the top floor
The summit is easily accessible, with a walk of approximately 15 minutes.
Event Information
Komakiyama hosts various events throughout the year. Seasonal events include a cherry blossom festival in spring and autumn foliage illuminations.
Regular on-site explanations of archaeological excavations are also held, providing opportunities to directly observe the latest research findings. Event information can be found on the Komaki City Tourism Association website and the official Komaki City website.
Future Development Plans for Komakiyama Castle
Komaki City is formulating a long-term development plan to preserve and utilize the Komakiyama historical site. Efforts are underway to balance the preservation and public access of the remains while continuing archaeological excavations.
In 2024, the main approach road was completed, allowing visitors to see the castle in a state closer to its original appearance. Further restoration of the stone walls of the main enclosure and development of the baileys are planned, and it is expected that the full scope of Komakiyama Castle will be further revealed.
Summary
Komakiyama Castle was the first full-fledged castle built by Oda Nobunaga, an innovative fortress with stone walls and a well-planned castle town. Although it was only used for four years, it had a significant impact on subsequent Japanese castle architecture and urban policy.
During the Battle of Komaki-Nagakute, it again became a historical stage as Tokugawa Ieyasu’s headquarters, making it a valuable historical site with layers of remains from both the Nobunaga and Ieyasu eras. Thanks to ongoing archaeological excavations, new discoveries continue to be made, further increasing the historical value of Komakiyama Castle. When you visit Aichi Prefecture, be sure to visit Komakiyama Castle and experience the atmosphere of the Sengoku period. By walking on the historical stage where two great figures of Japan, Oda Nobunaga and Tokugawa Ieyasu, were involved, you will be able to experience living history that you cannot learn from textbooks.
