The Siege of Iibama Castle occurred in Tenshō 2 (1574) near the end of the Sengoku period.  In this battle, Takeda forces attacked Tōyama Tomonobu (aligned with the Oda clan) at Iibama Castle in the Tōyama manor of the Ena District of Mino Province.  Iibama Castle was the closest defensive position built to protect the main base of the Tōyama clan at Iwamura Castle.

Background

The Tōyama manor was one of the demesne granted by Minamoto no Yoritomo to Katō Kagekado, a senior retainer of the Kamakura bakufu, for his contributions during the establishment of the Kamakura bakufu.  Tōyama Kagetomo (the eldest son of Katō Kagekado) was the first-generation head of the Tōyama clan.  Thereafter, from their base at Iwamura Castle, the Tōyama governed the Tōyama manor but descendants separated within the manor and formed cadet families.  One of these families was the Iibama-Tōyama clan.

In 1572, upon orders of Takeda Shingen, a retainer named Akiyama Torashige (Nobutomo) led forces from Inadani in Shinano Province to invade Mino and capture Iwamura Castle from the Tōyama clan.  This is known as the Siege of Iwamura Castle.  Oda Nobunaga positioned many fortresses around Iwamura Castle and dispatched Oda forces to these locations to await the opportunity to recapture Iwamura Castle.

In the fourth month of 1573, Takeda Shingen died while traveling from Mikawa Province back to his home base in Kai Province.

Invasion of eastern Mino

In 1574, Takeda Katsuyori led 30,000 soldiers and invaded eastern Mino, launching attacks against the Eighteen Ancillary Castles of the Tōyama.  The Takeda forces toppled the castles one after another including Naegi, Kano (Tsuruga), Busetsu, Imami, Adera, Magome, Ōi, Nakatsugawa, Tsurui, Kōta, Setozaki, Futta, Kushiwara, and Akechi castles.

In the course of these attacks, the Atera-Tōyama and Agi-Tōyama families were extinguished.

Oda Nobunaga dispatched an army of 30,000 troops led by Oda Nobutada and Akechi Mitsuhide to Mount Tsuruoka to establish a base and confront Katsuyori.  These forces pulled back after their road of retreat was threatened by Yamagata Masakage of the Takeda army.  During this period, seventeen of the eighteen castles were toppled up to Akechi Castle.  This is known as the Siege of Akechi Castle.

In the end, Iibama Castle was the only one remaining.  On the front lines at Iibama Castle, the two sides entered into a stalemate so two chief retainers of the Takeda, namely, Baba Nobuharu and Naitō Masatoyo, advised Katsuyori that the forces pull back to Kai.  Meanwhile, members of a new unit of rōnin, or wandering samurai, including Nawa Murinosuke, Ii Yashiemon, and Gomi Yosobei, requested out of a sense of duty permission for their unit to assault and capture Iibama Castle.  Other units comprised of hatamoto and tozama criticized the chief retainers on the grounds that Iibama Castle would become an intelligence base for the enemy forces and further asserted that allowing the rōnin unit to topple the castle would harm their reputation in the view of those in other provinces. 

As a result, upon the advice of Nagasaka Mitsukata and Atobe Katsusuke, a decision was made to continue the assault.  The vanguard forces surrounding the castle then broke-down the doors to the castle and charged in, capturing the base.  In a military chronicle known as the Kōyō-Gunkan, fourteen mounted soldiers dispatched by Nobunaga from Kawanakajima along with a garrison of over 350 soldiers were all killed while the commander of the castle, Iibama Uemon (surmised to refer to Tōyama Tomonobu or Tōyama Nobutsugu) was captured alive in the castle storehouse.  As the Takeda army returned to their base at Tsutsujigasaki in Kai, the ashigaru, or foot soldiers, composed a song that wove-in the names of five castles captured from the Oda.

Following its capture, Iibama Castle was abandoned.