The origins of the Iwabitsu Castle are uncertain, but it is believed to have been built by the local Agatsuma clan sometime in the 13th century. During the
Muromachi period, it was held by the Saitō clan, another local warlord. However, in the early
Sengoku period, it was captured by
Sanada Yukitaka, who had expanded from Shinano Province into northern
Kōzuke Province with the backing of his overlord,
Takeda Shingen. The Saitō clan had turned to
Uesugi Kenshin of
Echigo Province for assistance, but due to the distance from Echigo and the stratagems employed by the Sanada, the castle fell in 1563.
Sanada Masayuki used Iwabitsu Castle as his base to continue his expansion into northern Kōzuke, capturing
Numata Castle in 1579. He also rebuilt the Iwabitsu
jōkamachi into a fortified
shukuba by surrounding the entire town with a series of forts and gates, similar to the layout which he later employed when designing the new stronghold for the
Takeda clan at
Shinpu Castle as few years later. After the fall of the Takeda clan in 1582, Sanada Masayuki had planned to provide refuge for
Takeda Katsuyori at Iwabitsu Castle, but Katsuyori was unable to reach it due to treachery by some of his remaining retainers and committed
seppuku. The famed
samurai Karasawa Genba was an officer at the castle. Following the establishment of a stable regime under
Toyotomi Hideyoshi, Iwabitsu and Numata were awarded to
Sanada Nobuyuki, while his father Masayuki retained
Ueda Castle. Following the death of Toyotomi Hideyoshi, Sanada Masayuki remained loyal to
Toyotomi Hideyori and his regent
Ishida Mitsunari, whereas Sanada Nobuyuki, sided with
Tokugawa Ieyasu. With the victory by Tokugawa forces at the
Battle of Sekigahara in 1600, Sanada Nobuyuki was confirmed in his holdings in northern Kōzuke, but due to the
Tokugawa shogunate’s rule of “one domain – one castle” in 1615, Iwabitsu Castle was abolished. The
jōkamachi survived as
post station on the highway, but was relocated closer to the Agatsuma River. At present, nothing survives of the original castle. The entrance to the site is approximately 30 minutes on foot from
Gunma-Haramachi Station on the
JR East Agatsuma Line, followed by another 30 minute hike up the side of the mountain to reach the location of the
inner bailey. Iwabitsu Castle was listed as one of the
Continued Top 100 Japanese Castles in 2017. ==See also==