What Kind of Castle Was Nanao Castle?
Nanao Castle was a mountain fortress built by the Masuda clan after they entered Iwami Province during the Kamakura period. The exact date of construction remains uncertain, but it is traditionally said to have been established in 1193 by Masuda Kanetaka, the fourth head of the clan.
The castle occupied an extensive Y-shaped ridge stretching approximately 600 meters from north to south. More than 40 enclosures, known in Japanese as kuruwa, were arranged across the mountain.
Its defenses included cut ditches, earthen embankments, and distinctive groups of ridged dry moats. These features made effective use of the natural mountain terrain and created a formidable defensive system.
Although mountain castles are often imagined as places used only during times of war, archaeological excavations at Nanao Castle have revealed building foundations, garden remains, and tiled structures. These discoveries indicate that the castle was also a place where the lord and his retainers lived their everyday lives.
Nanao Castle During the Sengoku Period
During the later Sengoku period, the Masuda clan became increasingly involved in the conflicts that shaped western Japan. Masuda Fujikane, the 19th head of the clan, undertook major improvements to Nanao Castle in preparation for conflict with the powerful warlord Mori Motonari.
Fujikane is believed to have moved from Miyake Odoi to Nanao Castle together with his retainers. As a result, Nanao Castle became more than a defensive stronghold. It also served as an important center of politics and daily life during the Sengoku period.
Fujikane later became a vassal of the Mori clan, and his son Masuda Motoyoshi moved the family residence back to Miyake Odoi. Following the Battle of Sekigahara and the subsequent reduction of the Mori domain, the Masuda clan was transferred to Susa in present-day Yamaguchi Prefecture.
Nanao Castle was then abandoned, bringing its role as the center of Masuda rule to an end.
Panoramic Views from the Castle Summit
One of the greatest attractions of the Nanao Castle Site is the view from the former main enclosure.
From approximately 118 meters above sea level, the Masuda Plain stretches out below, with the blue waters of the Sea of Japan visible beyond it. Standing here, it is easy to imagine how the castle’s inhabitants could observe the surrounding territory from this strategic vantage point.
Today, the site can be explored as a hiking destination, allowing visitors to combine a walk through nature with an exploration of medieval Japanese history.
Sumiyoshi Shrine — Guardian of Nanao Castle
Located on the mountainside within the former castle grounds, Sumiyoshi Shrine held a special significance for the Masuda clan. It was traditionally revered as the guardian deity of Nanao Castle.
According to tradition, the shrine’s history dates back to Kunikané, the first head of the Mikamoto, or Fujiwara, family. When he was traveling to Iwami Province to take up his official post, his ship encountered a severe storm at sea.
He prayed to Sumiyoshi, a group of Shinto deities associated with the sea and safe navigation, and is said to have reached Iwami safely. In gratitude, Kunikané invited the deity to his new home and established a shrine.
Later, when Masuda Kanetaka, the fourth head of the Masuda clan, moved to Masuda and built Nanao Castle, the Sumiyoshi Shrine that had stood at Kamikō was reportedly relocated to the mountainside of Mount Nanao. There, it became the castle’s guardian shrine.
The Four Deities of Sumiyoshi Shrine
Sumiyoshi Shrine enshrines the three Sumiyoshi deities, traditionally associated with the sea, maritime travel, and protection of sailors: Uwatsutsunoo-no-Mikoto, Nakatsutsunoo-no-Mikoto, and Sokotsutsunoo-no-Mikoto.
In 1513, Masuda Munekane, the 17th head of the clan, visited Sumiyoshi Taisha in Osaka and brought back Empress Jingu, also known as Okinaga-Tarashihime-no-Mikoto, as an additional deity to be enshrined here.
Because of these connections with maritime deities, the shrine was associated not only with shipping, fishing, and safe sea travel, but also with protecting the castle and the territory governed by the Masuda clan.
Sumiyoshi Shrine from the Edo Period Onward
Masuda Motoyoshi, the 20th head of the clan, is said to have rebuilt the shrine buildings after safely returning from the Japanese invasions of Korea in the late 16th century, as an expression of gratitude.
The present main shrine building was constructed in 1664 under the Matsudaira family, lords of Hamada Domain. Repairs and improvements were carried out at various times afterward.
In 1968, a worship hall for distant prayer, known as a yōhaiden, was built. Further restoration of the main shrine and construction of a new worship hall were carried out in 1975 to commemorate Emperor Showa’s golden wedding anniversary and 50 years on the throne.
Archaeological Discoveries Reveal Medieval Life
Excavations at the Nanao Castle Site have uncovered numerous archaeological features and artifacts that shed light on life within the medieval castle.
At the former main enclosure, archaeologists discovered stone foundations and the remains of a gate. At the second enclosure, they found the remains of a garden and buildings supported by stone foundations.
Large quantities of ceramics have also been recovered, including Chinese-made ceramics. These artifacts indicate that the people living at Nanao Castle had access to sophisticated goods and participated in cultural exchanges that extended beyond the immediate region.
Particularly notable is the large quantity of small unglazed ceramic vessels known as kawarake discovered in the main enclosure. Such vessels were used for drinking and in ceremonial settings, suggesting that Nanao Castle served not only as a military stronghold but also as an important center for political activities and formal rituals.
Where Nature and History Meet
The area around Nanao Castle preserves numerous traces of its medieval defensive system, including ditch remains, dry moats, and former wells. Unlike castles dominated by stone walls, Nanao Castle made extensive use of the natural contours of the mountain, a characteristic feature of many medieval Japanese mountain fortresses.
At the foot of the mountain, visitors can also find traces of former waterways and moats that made use of an old river channel, as well as graves associated with generations of the Masuda clan.
Together, these remains allow visitors to explore the castle not simply as an isolated ruin but as part of a wider historical landscape that once included residences, religious sites, waterways, roads, and communities.
A Historic Destination with Magnificent Views
Sumiyoshi Shrine and the Nanao Castle Site are important cultural heritage sites that preserve the story of medieval Masuda. Exploring the mountain while looking across the same landscape once observed by medieval warriors offers a vivid sense of connection with the past.
Mount Nanao is surrounded by seasonal natural scenery, making the area suitable for both hiking and historical exploration. Visitors to Masuda can climb the mountain, explore the remains of Nanao Castle, and pay their respects at Sumiyoshi Shrine while discovering the history of the Masuda clan and the medieval world of Iwami.