* Image is for illustrative purposes only.Iwabitsu Castle
岩櫃城
Iwabitsu Castle is a historic castle in Kantō dating from the Ancient mountain fortress; captured 1563 by Sanada Yukitaka on Takeda Shingen's orders; became the Sanada clan's most important base in Kōzuke Province (Gunma), whose lord was Saitō Norihiro (Uesugi side) → Takeda Shingen (captured) → Sanada Yukitaka / Masayuki (Sanada Ueno Province base).
Overview
Iwabitsu Castle is a mountain castle located in Higashi-Agatsuma Town, Agatsuma District, Gunma Prefecture, known as an impregnable stronghold that maximizes the use of the steep rocky peaks of Mt. Iwabitsu at 802 meters elevation. It is counted as one of the three "indestructible castles of Takeda" (Takeda Sanken-jō)—namely, Iwatono Castle in Kai, Kunō Castle in Suruga, and Iwabitsu Castle in Kōzuke Province (Gunma).
The castle's history traces back to the Kamakura and Northern and Southern Courts periods, but reached its zenith under Sanada clan control during the Sengoku period. In Eiroku 6 (1563), Takeda Shingen ordered Sanada Yukitaka—later known as "Seme-Danjō" (Attack-Danjō), a master of strategy and intrigue—to capture Iwabitsu Castle. Yukitaka is said to have taken it not by frontal assault but through "rōraku/naiō" (internal subversion)—a stratagem to turn the castle's defenders—transmitted as the first great enterprise exemplifying the Sanada clan's strategic intelligence.
Under Sanada Masayuki, Iwabitsu Castle became the most critical stronghold of Sanada control in Kōzuke Province (Gunma). Following the destruction of the Takeda clan in Tenshō 10 (1582), Masayuki made Iwabitsu Castle a bastion of Sanada independence and, surrounded by four major powers—Oda, Hōjō, Tokugawa, and Uesugi—preserved the Sanada clan through "hyōri hikyo" diplomacy—a flexible survival strategy of changing allegiance according to circumstances. As a branch castle of Numata Castle, it is said that Deura Tsushima-no-Kami, a senior retainer of the Sanada family, served as its castellan.
Iwabitsu Castle was depicted in the 2016 NHK taiga drama "Sanada Maru" as the stage where Yukimura first achieved political maturity, and as "Sanada's Castle" it gained nationwide renown.
Connection to Swords
The relationship between Iwabitsu Castle and Japanese swords comes down to its connection with the Sanada clan — a family of warriors emblematic of Japanese blade culture. Sanada Yukimura (Nobushige) is the Sengoku-period warrior most widely beloved in modern Japan, celebrated as "the mightiest commander" and "the finest samurai," and his popularity in swords and armor stands unparalleled. The scarlet armor (aka-gusoku) — a suit dyed deep crimson — associated with Yukimura, together with its accompanying swords, survives at Sanada Shrine (Ueda, Nagano), Osaka Castle tenshu, and other locations across Japan, each bearing high tourism and cultural value as "Sanada Yukimura's swords." Iwabitsu Castle is the place where Yukimura first appears in historical records as a "commander," and is positioned as the gateway into his world of swords. Sanada Masayuki, alongside his roles as strategist and diplomat, is said to have possessed deep expertise in blade connoisseurship. Among the Sanada family blades housed at the Sanada Treasure Hall (Matsushiro), works associated with Masayuki are also included, and Iwabitsu Castle and Matsushiro Castle (Kaizu Castle) — the two major strongholds of the Sanada clan — function as two focal points in the narrative of "Sanada swords." The Agatsuma region, where Iwabitsu Castle is situated, was also a hub of smithing culture in Kōzuke (Gunma). Kōzuke blade-smiths were known as "Jōshū-mono" (Kōzuke blades), primarily producing tachi and wakizashi that supplied the warrior class of the Kantō and Shinano regions. The Kōzuke forces under Sanada Masayuki's command are thought to have been equipped with armaments combining locally produced blades with high-quality imports from Sōshū and Bizen.
Highlights
- Mt. Iwabitsu (802m) — the sheer volcanic rock face behind the castle ruins, the natural defense of one of Takeda's three indestructible castles
- Main and secondary bailey earthworks — ramparts, dry moats, and terrace remnants on the steep mountainside
- Iwabitsu Castle Hot Spring Relaxation Hall — spa facility near the castle ruins, the tourist hub for Sanada heritage
- Sanada clan main castle ruins (Ueda City) — the predecessor of Ueda Castle built by Masayuki, forming the Sanada 'two-castle' circuit with Iwabitsu
- Kusatsu Onsen — approx. 45 min drive from Iwabitsu, Japan's premier hot spring resort in the Agatsuma region
- Haramachi (Higashi-Agatsuma) Sanada exhibits — visitor infrastructure developed after the 2016 taiga drama 'Sanada Maru'
* Opening hours and admission fees are subject to change. Please check the official website before visiting.