Complete Guide to Iimori Castle | History and Highlights of Miyoshi Nagayoshi’s Residence and One of Western Japan’s Largest Mountain Castles
What is Iimori Castle?
Iimori Castle is a Sengoku period mountain castle built on the summit of Mt. Iimori (elevation 314m), which straddles Daito City and Shijonawate City in Osaka Prefecture. Also known as “Iimoriyama Castle,” it is famous as the residence of Miyoshi Nagayoshi, who ruled the Kinai region during the Sengoku period.
The castle grounds extend approximately 700m from north to south and 400m from east to west, making it one of the largest castles in Western Japan. It was selected as one of the “Continued Top 100 Japanese Castles” (number 160) on April 6, 2017, and officially designated a National Historic Site on October 11, 2021. Even today, the remains of the castle, including baileys, stone walls, moats, and earthen bridges, are well-preserved, making it an extremely important site for studying the history of medieval castles.
Iimoriyama is located on the northern spur of the Ikoma Mountains, which run north-south along the border between Osaka and Nara Prefectures, and was a strategically important point overlooking the border between Kawachi and Yamato Provinces. This location was a crucial factor in Iimoriyama Castle’s function as a base for controlling the Kinai region.
History of Iimoriyama Castle
From Construction to Miyoshi Nagayoshi’s Entry
There are various theories regarding the construction period of Iimoriyama Castle, but it is believed that some kind of castle facility already existed during the Nanboku-cho period. In the Sengoku period, it is said that Kizawa Nagamasa, the deputy governor of Kawachi Province, built a castle on Iimoriyama.
In 1542 (Tenbun 11), the Battle of Taiheiji took place between Miyoshi Nagayoshi and Kizawa Nagamasa, and Kizawa Nagamasa was defeated and killed. After this battle, Iimori Castle is believed to have come under the influence of the Miyoshi clan.
The Era of Miyoshi Nagayoshi – The Castle of the Unifier of Japan
In November 1560 (Eiroku 3), Miyoshi Nagayoshi moved his base from Akutagawayama Castle (Takatsuki City, Osaka Prefecture) to Iimori Castle. During this period, Nagayoshi controlled the Five Provinces of Kinai (Yamato, Yamashiro, Kawachi, Settsu, and Izumi) and the Shikoku region, reigning as the “unifier of Japan,” effectively controlling the politics of the Muromachi Shogunate.
Nagayoshi extensively renovated and expanded Iimori Castle, developing it not only as a military base but also as a center of politics and culture. Linked verse gatherings and tea ceremonies were held within the castle, and the cutting edge of culture of the time flourished. The “History of Japan,” written by the Portuguese missionary Luis Frois, records that missionaries frequently visited Iimori Castle, and that some of the Miyoshi family’s retainers converted to Christianity. Nagayoshi died of illness at Iimori Castle in 1564 (Eiroku 7), at the age of 43. After his death, the power of the Miyoshi clan rapidly declined.
From the Era of Oda Nobunaga to the Abandonment of the Castle
After the death of Miyoshi Nagayoshi, Oda Nobunaga expanded his power in the Kinai region. Around 1570 (Genki 1), Iimori Castle came under the control of the Oda clan, and it is believed that Miyoshi Yoshitsugu, a vassal of Nobunaga, and later Araki Murashige, served as its lords.
In 1576 (Tensho 4), as Oda Nobunaga continued his war against Ishiyama Honganji (the Ishiyama War), the strategic importance of Iimori Castle declined. It is believed to have been abandoned around 1580 (Tensho 8). After that, Iimori Castle disappeared from the historical stage, leaving only ruins in the mountains.
Structure and Features of Iimori Castle
Overall Structure of the Castle
Iimori Castle is a large-scale mountain castle spread across a vast area of approximately 700m north-south and 400m east-west, centered on the summit of Mount Iimori. The castle grounds are broadly divided into a northern area and a southern area.
The northern area consists of a group of baileys that emphasized defense, with a complex arrangement of moats and earthworks to prevent enemy intrusion. The main bailey (Senjojiki) is located at the summit, and this was the center of the castle.
The southern area consists of a group of baileys that functioned as living spaces, and it is presumed that the residences of Miyoshi Nagayoshi and his retainers were located here. This area has many relatively flat baileys, making it a structure suitable for daily life and administrative work.
Stone Wall Techniques
One of the most distinctive features of Iimori Castle is the extensive use of stone walls throughout the entire castle. These stone walls predate those of Oda Nobunaga’s Azuchi Castle and are extremely valuable historical remains for understanding the stone-building techniques of the mid-Sengoku period.
The stone walls were mainly constructed using the nozurazumi technique, a method of stacking natural stones as they are. The height varies depending on the location, but some sections reach a maximum of 3-4 meters. Local granite was used for the stonework, and many sections of the stone walls remain in good condition today.
Enclosures and Moats
Dozens of enclosures of varying sizes have been identified at Iimori Castle. The main enclosures include the following:
- Senjojiki (Main Enclosure): The most important enclosure located at the mountaintop, believed to be the site of Miyoshi Nagayoshi’s residence.
- Ninokuruwa: The second most important enclosure after the main enclosure.
- Sannomaru: A key defensive enclosure.
- Other Enclosures: Believed to have contained the residences of retainers, warehouses, and watchtowers.
Deep moats were constructed between the enclosures, serving to prevent enemy intrusion. These moats were dug perpendicularly across the ridges, reaching depths of over 10 meters in some places. Multiple earthen bridges crossing the moats have also been identified, providing clues to the movement within the castle.
Structure of the Castle Gate (Koguchi)
Several castle gate (koguchi) sites have been identified at Iimori Castle. The castle’s entrances are not simple, straight passages, but rather feature curved “staggered entrances” designed to make enemy intrusion difficult, and “square entrances” that allow attacks from both sides. These are important remains that demonstrate the development of castle construction techniques in the late Sengoku period.
Highlights of Iimori Castle
Senjojiki (Main Enclosure)
Located at the summit of Mount Iimori, Senjojiki is the central area of Iimori Castle and its most important highlight. Spanning approximately 3,000 square meters, it is believed to have been the site of Miyoshi Nagayoshi’s residence. Currently a flat open space, traces of stone walls remain around it.
From Senjojiki, you can enjoy a panoramic view of the Osaka Plain, and on a clear day, you can see Osaka Castle, Osaka Bay, and even Awaji Island. This excellent view is likely one of the reasons Iimori Castle was chosen as a base for controlling the Kinai region.
Stone Walls
The stone walls remaining throughout Iimori Castle are a must-see. Numerous well-preserved stone walls exist, particularly around the main enclosure and in the southern area’s baileys. These walls, built using the nozurazumi (rough-stone masonry) technique, are valuable historical remains that offer a direct glimpse into the castle-building techniques of the Sengoku period.
Recent surveys have revealed that parts of the stone walls have been restored and improved, making them easier to view. Information boards are also installed in front of the walls, allowing visitors to learn about their historical value.
Moats and Earthen Bridges
The moats located throughout the castle are important historical remains for understanding the defensive functions of Iimori Castle. In particular, multiple large moats are arranged in a series in the northern area, creating a structure that effectively prevented enemy intrusion in multiple layers.
Looking up from the bottom of the moats, one is overwhelmed by their depth and steepness. Furthermore, the earthen bridges built to cross the moats are also well-preserved, allowing visitors to experience the movement within the castle at that time.
Arrangement of the Enclosures
Iimori Castle features numerous enclosures of varying sizes arranged in a stepped pattern. Understanding this overall layout allows for a better understanding of the structure of a Sengoku period mountain castle. Each enclosure has an explanatory sign, allowing visitors to learn about its role and characteristics.
The enclosures in the southern area, in particular, are relatively flat and spacious, clearly indicating their function as living spaces. It is likely that Miyoshi Nagayoshi and his retainers lived their daily lives and conducted their official duties here.
Observation Spots
Because Iimori Castle is located on a mountaintop at an altitude of 314m, there are many excellent observation spots. From the main enclosure’s Senjojiki, you can see the entire Osaka Plain; from the northern enclosures, you can see towards Kyoto; and from the southern area, you can see towards Nara.
Perhaps Miyoshi Nagayoshi, during the Sengoku period, gazed upon this view while dreaming of unifying Japan. Modern visitors can also feel the romance of history by gazing upon the same scenery.
Access to Iimori Castle and Climbing Routes
Access Methods
Access by Train
There are several trailheads to Iimori Castle, but the most common routes are as follows:
- Nozaki Kannon Route (Daito City Side)
- Get off at Nozaki Station on the JR Gakken Toshi Line, and walk for about 10 minutes to Nozaki Kannon (Jigenji Temple).
- From Nozaki Kannon, take the hiking trail for about 60-90 minutes to the summit.
- Shijonawate Shrine Route (Shijonawate City Side)
- Get off at Shijonawate Station on the JR Gakken Toshi Line, and walk for about 15 minutes to Shijonawate Shrine.
- From Shijonawate Shrine, take the hiking trail for about 60-90 minutes to the summit.
Access by Car
There are parking lots around Nozaki Kannon and Shijonawate Shrine, but they can get crowded on holidays. There is also a forest road that allows you to drive close to the trailhead, but the road is narrow, so caution is advised for general vehicle traffic.
Climbing Route and Estimated Time
Climbing Iimori Castle requires mountain climbing equipment and physical fitness. The elevation difference is approximately 250-300m, and you should expect to spend 2-3 hours round trip.
Recommended Route
- Enter the hiking trail from Nozaki Kannon or Shijonawate Shrine.
- Climb while viewing several bailey remains and stone walls along the way.
- Arrive at Senjojiki (main bailey) at the summit.
- Visit the remains in the north and south areas.
- Descend via the same route or a different route.
Notes
- The hiking trail is well-maintained, but there are many steep slopes and stairs, so athletic shoes or trekking shoes are essential.
- Take precautions against the heat in summer and warm clothing in winter.
- Bringing drinking water and snacks is recommended.
- Be careful as the ground can be slippery during and after rain.
- There are no shops or toilets near the summit, so please prepare in advance.
Continued Top 100 Japanese Castles Stamp
Iimori Castle is selected as one of the “Continued Top 100 Japanese Castles,” and many people visit to collect stamps. The stamp locations are as follows:
- Daito City Historical and Folk Museum (3-6-1 Nozaki, Daito City)
- Shijonawate City Historical and Folk Museum (3-7 Tsukawaki-cho, Shijonawate City)
Both facilities have exhibits related to Iimorijo Castle, and visiting them before climbing the castle will deepen your understanding. It is recommended to check opening hours and closing days in advance.
Iimorijo Castle and Miyoshi Nagayoshi
Miyoshi Nagayoshi, the “First Unifier of Japan”
Miyoshi Nagayoshi (1522-1564) was a warlord who ruled the Kinai region during the Sengoku period and is sometimes called the “first unifier of Japan.” He was born in Awa Province (present-day Tokushima Prefecture) as the son of Miyoshi Motonaga.
Nagayoshi rose to prominence at a young age and served Hosokawa Harumoto, but eventually came into conflict with his lord. In 1549, Nagayoshi defeated Hosokawa Harumoto at the Battle of Eguchi, seizing control of the Kinai region. Subsequently, he supported Ashikaga Yoshiteru, the 13th Shogun of the Muromachi Shogunate, and led the government, bringing the five Kinai regions and eastern Shikoku under his control.
Nagayoshi was known not only for his military prowess but also as a man of culture. He loved linked verse poetry and the tea ceremony, and a cultural salon-like space was formed at Iimori Castle. He was also tolerant of Christian missionaries, and some of his retainers were baptized.
Reign at Iimori Castle
In 1560, Nagayoshi entered Iimori Castle and used it as his base to govern the Kinai region. Iimori Castle functioned not merely as a military base, but as a center of politics, diplomacy, and culture.
Nagayoshi hosted linked verse poetry gatherings at Iimori Castle and interacted with the cultural figures of the time. Furthermore, according to the records of Luis Frois, missionaries visited Iimori Castle and engaged in Christian evangelism. It is said that some of the retainers of Miyoshi Jikkyu, Nagayoshi’s younger brother, converted to Christianity.
However, Nagayoshi’s later years were marked by a series of misfortunes. In 1561, his younger brother Miyoshi Jikkyu was killed in battle, and in 1563, his eldest son, Miyoshi Yoshioki, died young from illness. These misfortunes took a toll on Nagayoshi’s mind and body, and the following year, 1564, Nagayoshi himself died of illness at Iimori Castle.
Significance of the Miyoshi Regime
The Miyoshi Nagayoshi regime occupies an important position in Japanese history because it unified the Kinai region before Oda Nobunaga’s unification of Japan. Nagayoshi, while supporting the Shogun of the Muromachi Shogunate, reigned as a “ruler of the land,” wielding de facto power. This form of governance is believed to have influenced the later political administrations of Oda Nobunaga and Toyotomi Hideyoshi.
Furthermore, Nagayoshi constructed Iimori Castle, a large-scale mountain castle extensively using stone walls, paving the way for later modern castles. Magnificent castles such as Azuchi Castle and Osaka Castle can be said to have developed from the construction techniques of Iimori Castle.
Investigation and Development of Iimori Castle
Results of Archaeological Excavations
Continuous archaeological excavations are being conducted at the Iimori Castle site by Daito City and Shijonawate City. Previous investigations have yielded the following results:
- Detailed surveys of the entire castle grounds have revealed the layout of baileys and moats.
- The structure and construction techniques of the stone walls have been elucidated, revealing the development process of castle construction technology in the mid-Sengoku period.
- Excavated pottery and roof tiles have provided insights into daily life and cultural exchange within the castle.
- The uses of the baileys and the division of functions within the castle are gradually being clarified.
These research findings support the idea that Iimori Castle functioned not merely as a military base, but as a center of politics, economy, and culture.
National Historic Site Designation and Preservation Activities
On October 11, 2021, the Iimori Castle ruins were officially designated as a National Historic Site. This will further advance the preservation and utilization of the castle ruins.
Daito City and Shijonawate City have jointly formulated the “Iimori Castle Ruins Preservation and Utilization Plan” and are proceeding with the following initiatives:
- Preservation and restoration work of the ruins
- Development of hiking trails and viewing paths
- Installation of explanatory signs and guide maps
- Cleaning and guiding activities by local volunteers
- Utilization in school education and lifelong learning
- Utilization as a tourist resource and promotional activities
Future Outlook
The development of the Iimori Castle Ruins is currently ongoing. The following initiatives are planned for the future:
- Restoration and public opening of major stone walls
- Recreation of the castle in its heyday using virtual reality (VR) technology
- Establishment of a visitor center
- Implementation of regular guided tours
- Holding of historical events and experiential programs
Through these initiatives, it is hoped that the Iimori Castle Ruins will become more familiar to a wider audience and be utilized as a place to learn about the history of the Sengoku period.
Attractions Around Iimori Castle
Nozaki Kannon (Jigenji Temple)
Nozaki Kannon, one of the trailheads to Iimori Castle, is officially known as Jigenji Temple and is an ancient temple said to have been founded by Gyoki during the Tenpyo-Shoho era (749-757). Its principal image, an eleven-faced Kannon statue, is designated as an Important Cultural Property, and a large-scale festival called “Nozaki Mairi” is held every May.
From the temple grounds, you can enjoy a panoramic view of the Osaka Plain, and it is also known as a famous spot for cherry blossoms and autumn leaves. It’s an ideal spot to visit before or after climbing to Iimori Castle.
Shijonawate Shrine
Shijonawate Shrine, located at the trailhead on the Shijonawate City side, is a shrine dedicated to Kusunoki Masatsura, a samurai from the Nanboku-cho period. Founded in 1890 (Meiji 23), the shrine grounds contain a bronze statue of Kusunoki Masayuki and the tomb of the young Kusunoki Masayuki.
The shrine is surrounded by a lush forest, creating a tranquil atmosphere. It’s a good idea to visit the shrine and pray for safety before climbing to Iimori Castle.
Daito City Historical and Folk Museum / Shijonawate City Historical and Folk Museum
Both city museums have permanent exhibitions on Iimori Castle. They display artifacts unearthed during archaeological excavations, a reconstructed model of the castle, and materials related to Miyoshi Nagayoshi, allowing visitors to learn about the history of Iimori Castle in detail.
In particular, visiting these museums before climbing the castle will allow you to understand the castle’s structure and historical background before viewing the remains, making for a more fulfilling experience.
Important Points When Visiting Iimori Castle
Clothing and Equipment
Climbing to Iimori Castle is a serious mountain climb, so please prepare the following equipment:
- Shoes: Athletic shoes or trekking shoes (sandals and heels are not allowed)
- Clothing: Comfortable clothing, warm clothing and rain gear appropriate for the season
- Items to Bring: Drinking water (500ml or more recommended), towel, hat, sunscreen, insect repellent spray
- Other: Hiking poles, first-aid kit, mobile phone (for emergencies)
Seasonal Precautions
- Spring (March-May): The weather is pleasant and it’s the best season to visit the castle. Cherry blossoms and fresh greenery are beautiful. However, those with hay fever should take precautions.
- Summer (June-August): The heat and humidity are severe, so be careful of heatstroke. Early morning or evening visits are recommended. Insect repellent is essential as there are many insects.
- Autumn (September-November): The autumn leaves are beautiful, making it the best season to visit the castle. However, the sun sets early, so be mindful of your time.
- Winter (December-February): The air is clear and the views are excellent. However, warm clothing is essential. Avoid climbing the castle when there is snow or ice.
Safety Precautions
- Avoid climbing the castle alone; please travel in groups whenever possible.
- If the weather deteriorates, do not force yourself to continue; turn back.
- There are areas where cell phone signals do not reach, so please inform your family or others of your climbing plans in advance.
- Be careful of wild animals (wild boars, venomous snakes, etc.).
- Do not damage the ruins or climb on the stone walls.
- Please take all your trash with you.
Cultural Value of Iimorijo Castle
Center of Politics and Culture in the Sengoku Period
Iimorijo Castle was not merely a military base, but also functioned as a center of politics and culture during the Sengoku period. Miyoshi Nagayoshi held renga (linked verse) gatherings at Iimorijo Castle and interacted with leading cultural figures of the time. Tea ceremonies were also popular, and cutting-edge culture flourished there.
Luis Frois’s “History of Japan” records that missionaries visited Iimorijo Castle and engaged in Christian evangelism. Nagayoshi showed a tolerant attitude towards religion and actively embraced contact with Western culture.
This cultural openness is thought to have influenced the policies of Oda Nobunaga later on, and Iimorijo Castle occupies an important position in Japanese cultural history.
Innovation in Castle Construction Techniques
Iimorijo Castle was a groundbreaking fortress in its extensive use of stone walls throughout its entire structure. While previous mountain castles primarily relied on earthen ramparts and moats for defense, Iimorijo Castle actively employed stone walls.
This stone wall technology later developed into early modern castles such as Oda Nobunaga’s Azuchi Castle and Toyotomi Hideyoshi’s Osaka Castle. Iimorijo Castle is an important site that represents the transitional period from medieval mountain castles to early modern flatland castles.
Importance of Medieval Castle Research
The Iimorijo Castle site is an extremely important site for studying the history of medieval castles. As one of the largest castles in western Japan, its structure, with its clearly separated defensive facilities and living spaces, provides valuable clues to understanding the development of castles during the Sengoku period (Warring States period).
Furthermore, artifacts such as pottery and roof tiles unearthed during excavations reveal the lifestyle, culture, and trade practices of the time. These research findings have made a significant contribution to the study of Japanese medieval history.
Summary
Iimoriyama Castle is one of the largest mountain castles in western Japan, serving as the residence of Miyoshi Nagayoshi during the Sengoku period and a base for his control of the Kinai region. Built on Mount Iimoriyama (elevation 314m), the castle grounds extend approximately 700m north-south and 400m east-west, with numerous baileys, stone walls, and moats remaining in excellent condition.
In 2017, it was selected as one of the “Continued Top 100 Japanese Castles,” and in 2021, it was designated a National Historic Site. Excavations and restoration work are still ongoing, and it remains a valuable historical site where many people can experience the history of the Sengoku period.
Climbing to Iimori Castle is a serious mountain climb, but the views from the summit and the historical romance are well worth the effort. See for yourself the view that Miyoshi Nagayoshi, the “first unifier of Japan” during the Sengoku period, once saw.
When climbing, be sure to have appropriate equipment and preparations, and take safety precautions while thoroughly enjoying the history and remains of Iimori Castle. We also recommend visiting the Daito City Historical and Folk Museum or the Shijonawate City Historical and Folk Museum before or after your climb to learn more about the history of Iimori Castle.
