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
-
Kubota Castle
The founder of the castle is considered to be Satake Yoshinobu (1570–1633). Yoshinobu was one of the six great generals of Toyotomi Hideyoshi. During the Odawara Campaign of 1590, he took part in the siege of Oshi Castle under the command of Ishida Mitsunari, with whom Yoshinobu developed a good relationship.
-
Kavanhoe Castle
Kawanoe Castle is located on the small Wasi-yama hill near the port area of the Kawanoe district in the city of Shikokuchuo, occupying a central position along the northern coast of Shikoku Island. Kawanoe was also known as Butsuden Castle. The term “butsuden” in Japan refers to temple halls, and for this reason it is believed that a Buddhist temple once stood on the site before the castle was built. Due to its location at the junction of four provinces on Shikoku Island, Kawanoe held significant strategic importance and was repeatedly targeted by rival forces seeking military control over the region.
-
Yokote Castle
The founder of the castle is considered to be the Onodera clan. The Onodera were originally a minor clan from Shimotsuke Province and served Minamoto no Yoritomo (1147–1199), the founder of the first shogunate. The Onodera distinguished themselves in battle against the Fujiwara clan of the Ōshū branch and were rewarded with lands around Yokote. Around the 14th century, the Onodera moved to Yokote as their permanent residence. Their original stronghold was Numadate Castle, but after a series of clashes with the powerful Nambu clan, they relocated their base to the site of present-day Yokote Castle. It was likely during this time that the first fortifications appeared at the castle.
-
Wakayama Castle
Wakayama Castle was built in 1585, when Toyotomi Hideyoshi ordered his uterine brother, Hashiba (Toyotomi) Hidenaga, to construct a castle on the site of the recently captured Ota Castle. The purpose of this construction was to secure control over the likewise newly conquered Province of Kii. Following an already established tradition, Hidenaga entrusted the project to his castle-building expert, Todo Takatora. Takatora carefully inspected the future castle site, personally drew up several designs, created a model of the planned castle, and took part in the work of laying out the grounds (nawabari). For the construction he brought in more than 10,000 workers and completed the large-scale project within a single year, which was considered extremely fast by the standards of the time.
Toyama Castle
Toyama Castle is located almost in the very center of the former province of Etchū and is surrounded by a wide plain with a large number of rivers. The very first castle on the banks of the Jinzu River was built in 1543 by Jimbo Nagamoto. The Jimbo clan were vassals of the Hatakeyama clan and governed the western part of Etchū Province. The eastern part of the province belonged to their rivals, the Shiina clan, who were also Hatakeyama vassals. Beginning in the 15th century, the influence of the ancient Hatakeyama clan gradually weakened, and as a result, the Jimbo and the Shiina fought constant wars for control of the province. Meanwhile, the forces of the Ikkō-ikki movement periodically intervened, helping first one side and then the other.
Takada Castle
During the Sengoku period, the lands where Takada Castle would later be built were part of Echigo Province and were controlled by the Uesugi clan.
Kishiwada Castle
The celebrated 14th-century military commander Kusunoki Masashige (1294–1336), who owned extensive lands south of what is now the city of Osaka, ordered one of his vassals, Kishiwada Osamu, to build a fortified residence. This order was carried out around 1336. These fortifications became the first structures on the site of what would later become Kishiwada Castle. From the beginning, the castle stood in a strategically important location—roughly halfway between the cities of Wakayama and Osaka, south of the key port of Sakai. Because of this position, it changed hands several times during periods of warfare.
Kaminoyama Castle
Kamino-yama Castle stood at the center of an important logistics hub, in the middle of the Yonezawa Plain, which served as the gateway to the western part of the Tohoku region. Roads connecting the Aizu, Fukushima, and Yamagata areas intersected here.
