Siege of Inabayama Castle

What Happened

The siege of Inabayama Castle was fought between 13 and 27 September 1567, a two-week campaign that ended in a decisive victory for Oda Nobunaga’s combined forces. In the Japanese calendar, the fighting ran from the 1st to the 15th day of the eighth month in the 10th year of the Eiroku era (永禄, えいろく). The battle brought the Saitō clan, their vassals, and their allies under Nobunaga’s control, and it marked the final act in his campaign to conquer Mino Province.

The siege itself was short, but the outcome was total. Nobunaga’s army broke into the mountaintop castle, and the Saitō leadership collapsed. Many samurai leaders had already defected to Nobunaga before the fighting began, and others submitted willingly once the castle fell. The victory ended a rivalry between the Oda clan of Owari Province and the Saitō clan of Mino that had begun over twenty years earlier, when Nobunaga’s father, Oda Nobuhide, and the Saitō leader Saitō Dōsan first clashed.

Background

Nobunaga’s Mino campaign had been waged intermittently for six years before the siege. The Saitō clan held Inabayama Castle, a formidable mountaintop fortress, and their territory was both expansive and fertile. The Saitō leadership at the time of the siege was weak, and that weakness proved decisive. Saitō Tatsuoki, the clan head, failed to hold the loyalty of his samurai, and defections to Nobunaga accelerated in the months and years before the attack.

One of Nobunaga’s young retainers, Kinoshita Tōkichirō (木下藤吉郎, きのした とうきちろう) — later known as Toyotomi Hideyoshi — played a central role in the preparations. In the years leading up to the battle, he negotiated with local warlords to secure their support, ensuring that Nobunaga would have a ready-made army when the attack came. Tōkichirō also built a castle on the edge of Saitō territory to serve as a staging point for the assault. When the time came, he devised and personally led a bold plan: a commando-style raid into the castle to open its gates for the main attacking force. The plan worked, and the castle fell.

Why It Mattered

With the victory, Nobunaga took control of Mino Province and gained a large number of new supporters and resources. He had Inabayama Castle repaired and renamed it Gifu Castle (岐阜城, ぎふじょう), and it became his primary residence and military headquarters. From Gifu, he could expand north into the Hokuriku region and press his drive toward Kyoto. The castle served as his base until he moved to the partially completed Azuchi Castle in 1575.

The siege also mattered for the career of Kinoshita Tōkichirō. His negotiations, his staging castle, and his gate-opening raid raised his standing with Nobunaga considerably. The victory at Inabayama was therefore not only a turning point in Nobunaga’s unification of Japan but also an important step in Toyotomi Hideyoshi’s rise to power.

The Name in Japanese

The Japanese name for the siege is 稲葉山城の戦い, read いなばやまじょうのたたかい, and romanised as Inabayama-jō no Tatakai. It means “Battle of Inabayama Castle.”

Breaking it down character by character:

• 稲 (いな, ina) — “rice plant.” In this word it appears as part of the place name Inaba.
• 葉 (ば, ba) — “leaf.” Together with 稲, it forms 稲葉 (いなば, Inaba), the name of the mountain.
• 山 (やま, yama) — “mountain.” Inabayama is the mountain on which the castle stood.
• 城 (じょう, jō) — “castle.” This is the standard reading for 城 when it appears in castle names.
• の (no) — the possessive particle, meaning “of.” It links the castle name to the noun that follows.
• 戦い (たたかい, tatakai) — “battle” or “fight.” The verb form is 戦う (たたかう, tatakau), “to fight.”

So the full phrase is literally “the battle of Inabayama Castle.” The castle itself was later renamed Gifu Castle, but the battle keeps the older name because it took place before the renaming.

Key Figures

Oda Nobunaga (織田信長, おだ のぶなが) was the leader of the Oda clan of Owari Province and the commander of the attacking forces. The siege was the culmination of his six-year campaign against the Saitō clan, and his victory gave him control of Mino Province and a base for expansion toward Kyoto.

Saitō Tatsuoki (斎藤龍興, さいとう たつおき) was the head of the Saitō clan at the time of the siege. His weak leadership drove many of his samurai to defect to Nobunaga before the battle, and his defeat ended the Saitō clan’s hold on Mino Province.

Kinoshita Tōkichirō (木下藤吉郎, きのした とうきちろう) was a young retainer of Nobunaga who later became known as Toyotomi Hideyoshi. He negotiated alliances with local warlords, built a staging castle near enemy territory, and led the raid that opened Inabayama Castle’s gates. His role in the victory significantly raised his standing with Nobunaga.

Hachisuka Masakatsu (蜂須賀正勝, はちすか まさかつ) was a samurai associated with the campaign. He is recorded in connection with the conflict around Inabayama Castle.

Takenaka Shigeharu (竹中重治, たけなか しげはる) was another samurai linked to the siege. He is often remembered as a strategist, and his involvement in the events around Inabayama Castle is part of the battle’s recorded history.