The Battle of Iwamura Castle — Lady Otsuya, Akiyama Torashige, and the Fall of the Castle in the Mist

The Battle of Iwamura Castle: The Female Castellan and Takeda's Master Strategist

Iwamura Castle, located in the Tōnō region of Mino Province, was built on a mountaintop at an elevation of 717 m. It is counted among Japan's Three Great Mountain Castles, along with Bitchū Matsuyama Castle and Takatori Castle. It is known as the castle built at the highest elevation among the domain seats of the Edo period. It is said to have been built in the early Kamakura period by Tōyama Kagetomo, the eldest son of Katō Kagekado, a senior retainer of Minamoto no Yoritomo. Thereafter it served as the seat of the Tōnō Tōyama clan and became the central fortress of the Tōnō region. The castle, also known as Kirigajō, first became known nationwide through the struggle between the Takeda and Oda houses that unfolded from Genki 3 (1572) to Tenshō 3 (1575), and above all through the tragedy of its central figure, the "female castellan" Lady Otsuya.

Lady Otsuya Governs Tōnō

After the death of Tōyama Kagetō, lord of Iwamura Castle, his widow, Lady Otsuya, who was an aunt of Oda Nobunaga, held the castle as its female castellan and governed Tōnō. Nobunaga trusted his aunt deeply and sought to bring Tōnō within the Oda sphere of influence. He sent his own son, Gobōmaru, to the Tōyama family as an adopted heir. At that time, Tōnō was a border zone where the Takeda and Oda forces contended, and Iwamura Castle was a strategic stronghold at the front line. For Nobunaga, securing Tōnō was an essential step in fortifying the rear of his home provinces of Mino and Owari and in halting the Takeda advance. Even after her husband's death, Lady Otsuya, though a woman, displayed skill in managing her domain and bore heavy responsibility as the Oda side's representative in Tōnō. The castle's strength, built on a mountaintop 717 m high, had a scale and defensive capability suited to its role as the linchpin of that rule.

Akiyama Torashige's Persuasion and Marriage

In Genki 3 (1572), Takeda Shingen, as part of the Western Campaign, dispatched his senior retainer Akiyama Torashige (also known as Nobutomo) to attack Tōnō. Akiyama was counted among the Twenty-Four Generals of Takeda and was a valiant commander. He surrounded Iwamura Castle. Akiyama proposed terms of peace to Lady Otsuya. The condition was that if she herself became Torashige's wife, the lives of those holding out in the castle would be guaranteed. Unable to wait for relief from the Oda side, Lady Otsuya accepted this condition, and Iwamura Castle fell into Takeda hands without a major battle. Nobunaga is said to have been enraged on learning that his own son, Gobōmaru, whom he had sent to the Tōyama family as an adopted heir, had become a hostage of the Takeda side. However, because the Western Campaign was still underway, he could not immediately turn to counterattack. As a result of this affair, the balance of power across all of Tōnō tilted sharply in favor of the Takeda, and the eastern line of defense of the Oda domain was greatly shaken. Akiyama Torashige was a hereditary senior retainer of the Takeda house, known as a clever commander skilled in commanding the Shinano sakigata forces and in diplomatic negotiation. He was not merely a fierce warrior. His political skill in deftly employing peace negotiations and persuasion is also evident from the success of this marriage stratagem. Torashige's flexible strategic judgment played an important role in the Western Campaign. Ironically, however, the success of that persuasion provoked Nobunaga's fierce anger and also became one cause of the tragic outcome that followed. Tōnō, where Iwamura Castle stood, bordered the Oda family's home provinces of Mino and Owari. Losing this area meant a threat to Nobunaga beyond a mere loss of territory. Shingen's Western Campaign was a wide-ranging strategy that simultaneously pressed on Oda and Tokugawa territories from several directions, including Tōnō, Tōtōmi, and Mikawa. The capture of Iwamura Castle by Akiyama Torashige formed one wing of that strategy. Even after Shingen died of illness in Genki 4 (1573) and Katsuyori succeeded him, Iwamura Castle continued to function as the Takeda side's base for ruling Tōnō. However, the defeat at the Battle of Nagashino overturned its strategic advantage at the root.

Nobunaga's Wrath and the Recapture of Iwamura Castle

In the 5th month of Tenshō 3 (1575), Nobunaga defeated Takeda Katsuyori's army at the Battle of Nagashino. With the might of his musketeers, he dealt a crushing blow to the Takeda's elite cavalry corps. This victory caused Takeda military power to decline decisively. Riding this momentum, Nobunaga ordered his eldest son, Oda Nobutada, to recapture Iwamura Castle. Akiyama Torashige, under attack from Nobutada's army, surrendered on the condition that the lives of his soldiers and retainers would be spared. However, Nobunaga broke this promise. He is said to have executed Akiyama Torashige and Lady Otsuya in Gifu by the cruel method of upside-down crucifixion. This judgment, which spared not even his blood-related aunt, is still told today as an event symbolizing Nobunaga's ruthlessness and the height of Sengoku-era scheming. This execution, beyond a mere military victory, is thought to have carried a strong political meaning as a warning to those who had sided with the Takeda. The fate that Lady Otsuya ultimately accepted symbolized the ruthlessness of the Sengoku age, in which political strategy and blood ties were intricately intertwined. For Nobunaga, the recapture of Iwamura Castle had meaning beyond simply regaining a single castle. It became an important step in re-establishing Oda control over all of Tōnō.

Mino-den Swordsmiths and Weapons Culture of Tōnō

The Tōnō region, where Iwamura Castle is located, lies at the eastern edge of the Mino-den sword culture sphere centered on Seki. Mino-den is counted among the Gokaden, the five major traditions of Japanese swords. Mino's swordsmiths, including Kanemoto and Kanesada, forged many practical blades that "do not break, do not bend, and cut well," and they received immense support from Sengoku warlords. The annihilation of the Takeda's elite cavalry corps by the Oda and Tokugawa musketeers at the Battle of Nagashino was also an event symbolizing the tactical shift from close combat to long-range combat. At present, the Ena City Iwamura Historical Museum displays materials related to the Iwamura Domain, including illustrated maps of Iwamura Castle.

The Ruthlessness of the Sengoku Era Carved by Tragedy

The castle town of Iwamura still retains strong traces of its history as the stage of the struggle between the Takeda and Oda houses. Since the Edo period, the castle town, lined with sake breweries and long-established merchant houses, has been designated an Important Preservation District for Groups of Traditional Buildings, and it conveys the look of that era to the present day. The magnificent stone-wall complex that rises on the northeast side of the Honmaru, called Rokudan-kabe (the six-tiered wall), is thought to have been constructed in the late Edo period. Its scale and precision represent the very best of castle architecture. The Battle of Iwamura Castle was not merely a territorial dispute. It was an incident that condensed a human drama of the Sengoku age: the decision of a female castellan who tried to protect the castle and its people through a political marriage, and the merciless retaliation of her nephew Nobunaga, who would not permit it. This tragedy inscribed Iwamura Castle into history as the "castle of the female castellan." In the Edo period, several daimyō, including the Matsudaira and Niwa families, served as its lords, and the castle continued as Iwamura Domain until the late Edo period. Together with its stone walls, still wrapped in mist, the story of Lady Otsuya and Akiyama Torashige speaks to visitors of their unusual fate.

This series of assaults and contests over Iwamura Castle was not merely a military struggle for possession. As a case that condensed every element of Sengoku diplomacy, including political marriage, hostages, and betrayal, it has continued to draw strong interest from later historians and literary works. Walking through the castle ruins, one can today sense both the spirit of Lady Otsuya, who governed her domain as a female castellan, and the ruthlessness of the Sengoku age that toyed with her fate.