Iwabitsu Castle is a yamashiro-style (mountain) castle located atop Mount Iwabitsu in Higashiagatsuma, Gunma Prefecture, Japan. Recognized for its historical significance, its ruins have been protected as a National Historic Site since 2019.
Situated in northwestern Gunma Prefecture, the castle overlooked a key route through the Agatsuma River valley, a corridor connecting Takasaki to Shinano Province via the Shinshu Kaido and Torii Pass. This strategic location made it a vital stronghold for controlling regional travel and military movements.
The origins of Iwabitsu Castle remain uncertain, though it is believed to have been built by the Agatsuma clan in the 13th century. During the Muromachi period, it came under the control of the Saito clan, another local warlord. However, in the early Sengoku period, Sanada Yukitaka, with the backing of his overlord Takeda Shingen, captured the castle in 1563 after defeating the Saito clan, who had unsuccessfully sought aid from Uesugi Kenshin of Echigo Province.
Sanada Masayuki later used Iwabitsu Castle as his base to expand into northern Kozuke Province, capturing Numata Castle in 1579. He also fortified the surrounding jokamachi (castle town) with defensive structures, a strategy he later employed in the design of Shinpu Castle for the Takeda clan. After the fall of the Takeda in 1582, Masayuki planned to shelter Takeda Katsuyori at Iwabitsu, but Katsuyori was betrayed by his retainers and committed seppuku before reaching safety.
Under the Toyotomi regime, Iwabitsu and Numata were granted to Sanada Nobuyuki, while his father Masayuki retained control of Ueda Castle. Following the death of Toyotomi Hideyoshi, Masayuki remained loyal to Toyotomi Hideyori and Ishida Mitsunari, whereas Nobuyuki sided with Tokugawa Ieyasu. After the Tokugawa victory at the Battle of Sekigahara in 1600, Nobuyuki retained his holdings in northern Kozuke, but the one domain, one castle policy of the Tokugawa shogunate led to the dismantling of Iwabitsu Castle in 1615. The jokamachi survived as a post station but was relocated closer to the Agatsuma River.
Today, no structures from the original castle remain. Visitors can reach the site via a 30-minute walk from Gunma-Haramachi Station on the JR East Agatsuma Line, followed by a challenging 30-minute hike up the mountain to the former inner bailey.
In recognition of its historical importance, Iwabitsu Castle was included in the "Continued Top 100 Japanese Castles" list in 2017.
See also
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Numata Castle
Numata Castle, located in Numata, northern Gunma Prefecture, Japan, has a rich and complex history. During the late Edo period, it served as the residence of the Toki clan, who ruled the Numata Domain. Over the centuries, the castle changed hands multiple times and was the site of significant battles during the Sengoku period.
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Tsutsujigasaki Castle
Tsutsujigasaki Castle (Tsutsujigasaki Yakata) served as the fortified residence of the last three generations of the Takeda clan and is located in the heart of Kofu, Yamanashi Prefecture, Japan. Unlike traditional Japanese castles, it was not referred to as a "castle" in Japanese, as the Takeda clan famously believed in relying on their warriors as their true fortifications, stating, "Make men your castle, men your walls, men your moats." Designated a National Historic Site in 1938, the ruins are now open to the public and house the Takeda Shrine, a Shinto shrine dedicated to the deified spirits of the Takeda clan.
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Nagoya Castle
Nagoya Castle, originally built by the Owari Domain in 1612 during the Edo period, stands on the site of an earlier Oda clan castle from the Sengoku period. It became the centerpiece of Nagoya-juku, a significant castle town on the Minoji road, which connected two major Edo Five Routes: the Tokaido and the Nakasendo. In 1930, ownership of the castle was transferred to the city by the Imperial Household Ministry, establishing it as the focal point of modern Nagoya. Although partially destroyed in the Pacific War in 1945, the castle has undergone continuous restoration and preservation efforts since 1957.
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Matsushiro Castle
Matsushiro Castle, originally known as Kaizu Castle, is located in what was once Matsushiro town, now part of Nagano City. The site is recognized as a National Historic Site of Japan. Situated on the northern Shinano flatlands between the Chikuma River and a former riverbed that serves as a natural outer moat to the north, the castle and its surrounding town were prone to flooding due to their location.
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Fushimi Castle
Fushimi Castle, also known as Momoyama Castle or Fushimi-Momoyama Castle, is located in Fushimi Ward, Kyoto. Originally built by Toyotomi Hideyoshi between 1592 and 1594 as his retirement residence, the castle was destroyed by the 1596 Keichō–Fushimi earthquake and later rebuilt. However, it was demolished again in 1623, and its site now houses the tomb of Emperor Meiji. A replica of the castle was constructed nearby in 1964.
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Odawara Castle
Odawara Castle, located in the city of Odawara, Kanagawa Prefecture, Japan, is a reconstructed historical site with roots dating back to the Kamakura period (1185–1333). The current donjon (main keep) was rebuilt using reinforced concrete in 1960 on the stone foundation of the original structure, which was dismantled between 1870 and 1872 during the Meiji Restoration.
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Shinpu Castle
Shinpu Castle was a Japanese hirayama-style fortress from the Sengoku period, situated in what is now Nirasaki, Yamanashi Prefecture. It served as the main stronghold of warlord Takeda Katsuyori. Designated as a National Historic Site in 1973, the castle occupies a strategic position on a mountain with steep cliffs, overlooking the Kamanashi River to the west of Kofu, where Takeda Shingen’s Tsutsujigasaki Castle once stood.
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Takato Castle
Takato Castle, located in the city of Ina in southern Nagano Prefecture, Japan, was a notable stronghold during the Sengoku period. By the end of the Edo period, it was the residence of a cadet branch of the Naito clan, the daimyo of the Takato Domain. Also known as Kabuto Castle, it was originally constructed in the 16th century and is now mostly in ruins.
