Siege of Inabayama Castle

The Siege of Inabayama Castle — Nobunaga's Conquest of Mino and the Foundation of Tenka Fubu

In August of Eiroku 10 (1567), Oda Nobunaga, based in Owari Province (present-day Aichi Prefecture), finally seized Inabayama Castle, the strategic stronghold in Mino Province (present-day southern Gifu Prefecture), which he had long sought to conquer. This "Siege of Inabayama Castle" stands as one of the decisive battles that altered the course of the Sengoku period, and is positioned as the first major turning point in Nobunaga's campaign to unify Japan under his rule.

Inabayama Castle was a mountain fortress built atop Mount Kinkazan (329 meters above sea level), and was known as an "impregnable castle" owing to its natural defensive advantages and its commanding position overlooking the Nagara and Kiso rivers. The castle had once served as the base from which Saitō Dōsan, the "Viper of Mino," ruled the province, and was passed down to his son Yoshitatsu and grandson Tatsuoki.

The Long Prelude to Mino's Conquest — Saitō Dōsan's Will and Nobunaga's Determination

The tie between Nobunaga and Mino Province ran deep. Nobunaga's principal wife, Kicho (also called Nōhime), was the daughter of Saitō Dōsan, making Nobunaga the latter's son-in-law. Dōsan was killed by his eldest son Yoshitatsu (in Kōji 2, 1556), and it is said that on his deathbed he left a will bequeathing Mino Province to Nobunaga. Whether this will was genuine or not, the conquest of Mino became an essential objective for Nobunaga on both familial and strategic grounds.

From around Eiroku 2 (1559) onward, Nobunaga intensified his offensive against Mino, engaging Saitō Yoshitatsu (Tatsuoki's father) in several battles. But Yoshitatsu was a figure of both military prowess and strategic cunning, and Nobunaga found himself struggling in his efforts to conquer Mino during this period. When Yoshitatsu died suddenly in Eiroku 4 (1561) at the age of thirty-five, he was succeeded by his heir Saitō Tatsuoki, then only fourteen or fifteen years old. Tatsuoki lacked the capacity of his grandfather Dōsan or his father Yoshitatsu, and factional strife plagued the Saitō clan, creating an opportunity for Nobunaga.

Eiroku 7: Takenaka Hanbei's Occupation of Inabayama Castle — A Sign of Internal Turmoil

An important incident served as a prelude to the final assault on Inabayama Castle. In Eiroku 7 (1564), Takenaka Hanbei (Shigeyoshi), a young strategist of Mino, along with his brother Kyusaku and some sixteen companions, occupied Inabayama Castle. Moved by righteous indignation at the unjust treatment of his brother Kyusaku by Tatsuoki's close advisors, Hanbei accomplished the remarkable feat of launching a surprise assault on the supposedly impregnable Inabayama Castle with only several tens of men and securing control of it. After this, Hanbei returned the castle to Tatsuoki and withdrew into the mountains, but the incident demonstrated that Inabayama Castle could be captured by surprise assault with a small number of skilled troops. Later, Hanbei was earnestly recruited by Kinoshita Tōkichirō (Hideyoshi) and joined the Oda forces, eventually serving as Hideyoshi's strategist.

The Final Assault of Eiroku 10 — Kinoshita Tōkichirō's Decisive Role and Tatsuoki's Flight

In Eiroku 10 (1567), Nobunaga undertook the final phase of Mino's conquest. The crucial role was played by Kinoshita Tōkichirō, then a relatively young commander (the future Toyotomi Hideyoshi, at the time some thirty to thirty-one years old). Tōkichirō had cultivated internal supporters within the castle and executed a daring stratagem: leading a small force of selected men through the castle's rear gate (karamechi) under cover of darkness. The surprise assault succeeded, and chaos spread through the garrison. As Nobunaga's main force attacked from the front, Tōkichirō and his men created disorder from within, leaving Saitō Tatsuoki with no means of resistance. He fled by boat down the Nagara River to Ise Province. The Oda forces captured Inabayama Castle, bringing all of Mino Province under Nobunaga's control. After his flight, Tatsuoki continued his resistance to Nobunaga while wandering through Ise and Ōmi provinces. He is said to have died in battle at Tonezaka during Tenshō 1 (1573), fighting on the Asakura side.

The Renaming to Gifu Castle and "Tenka Fubu" — The Dawn of a New Era

Upon seizing Inabayama Castle, Nobunaga immediately began the development of the castle and its surrounding town. Most notably, he renamed the castle to Gifu Castle, and the town below it likewise became Gifu. The character 'gi' (岐) was drawn from Mount Qi (岐山) in China, the legendary origin of the Zhou dynasty, while 'fu' (阜) means a prosperous mound. This echoed the historical precedent of King Wen of Zhou, who unified the realm from Mount Qi. Nobunaga's grand ambition to unify Japan was embedded in this name.

Moreover, from this period onward, Nobunaga began using the seal Tenka Fubu ("to spread military rule throughout the realm" — in other words, to unify Japan through military force). This motto was an explicit declaration of Nobunaga's determination to unify Japan and represented a new value system of the Sengoku period — the assertion that practical power rather than ritual propriety would determine mastery of the realm. Gifu Castle became the base from which Nobunaga would pursue this agenda, and he deployed it as a political stage for negotiations with regional commanders, daimyo, and the imperial court and nobility.

The Connection to Blades — Mino's Swordsmiths and the Fame of Seki Forges

In considering the relationship between the Siege of Inabayama Castle and the culture of the sword, the most important fact is that Seki (in Mino Province, present-day Seki City, Gifu Prefecture) has long been renowned as a "city of swords" and is one of Japan's largest sword-producing centers. The history of the Seki forges extends back to the period of the Northern and Southern Courts (the fourteenth century), with tradition attributing its lineage to Kanemoto, a distinguished student of Masamune. By the Muromachi period, Seki smiths had achieved national renown, and their blades were celebrated for a cutting quality capable of "slicing through three layers of armor." During the Sengoku period, Mino continued to supply swords to both the Oda and Saitō forces as a major center of production.

The struggle over Inabayama Castle was not only a contest for control of Mino's economic and political power but also a struggle to secure access to the fine weapons produced by Seki smiths. When Nobunaga established control of Mino, the techniques and productive capacity of Seki smiths became part of the foundation supporting the Oda regime's military power. Tradition holds that Nobunaga himself favored swords made by Seki smiths, and during the Gifu Castle period he commissioned and collected blades from renowned masters throughout the realm. Records also show that Nobunaga's commanders received celebrated blades as rewards for their role in Mino's conquest, and the practice of presenting Seki swords as symbols of military achievement became established.

The Historical Significance of the Siege of Inabayama Castle — The Full Mobilization of the Campaign for Unification

The fall of Inabayama Castle was more than the conquest of a single castle and province; viewed in the broader context of the Sengoku period, it represented a distinctive historical turning point. With Nobunaga's acquisition of Mino — a vast and prosperous domain — following his rise from a regional lord of Owari, his campaign for national unification entered its decisive phase. In the following year, Eiroku 11 (1568), Nobunaga escorted Ashikaga Yoshiaki to Kyoto and established control over the capital and the Kinai region. Nobunaga's campaigns continued: the Battle of Anegawa in Eiroku 13 (Genki 1, 1570), the Battle of Mikatagahara in Genki 3 (1572), the Siege of Ichijōdani in Tenshō 1 (1573, which resulted in the destruction of the Asakura clan) and the fall of the Asai clan. All of these campaigns traced their origin to the conquest of Inabayama Castle in August of Eiroku 10.

Inabayama Castle — Gifu Castle — stands today as a symbol of Gifu City, with a reconstructed keep rising from the summit of Mount Kinkazan, bearing witness to Nobunaga's dream of Tenka Fubu. Each autumn, the Nobunaga Festival is held at the site of Nobunaga's former residence, drawing history enthusiasts from throughout Japan. The remains of Nobunaga's castle town that spread beneath Gifu Castle form the foundation of present-day Gifu's urban layout, still bearing witness to the significance of this place as a turning point in the Sengoku period.