Siege of Odani Castle

The Battle of Odani Castle: The Last Stand of Azai Nagamasa and Nobunaga's Conquest of Ōmi

In August 1573 (Tenshō 1), Oda Nobunaga launched a total assault on Odani Castle, the stronghold of the Azai clan in northern Ōmi Province, forcing Azai Nagamasa to take his own life and bringing the Azai to ruin. The "Battle of Odani Castle" was a pivotal moment on Nobunaga's path to the unification of Japan, and it was a crucial campaign that, by simultaneously eliminating the Azai and Asakura—the dominant powers of Ōmi and Echizen—solidified Nobunaga's control over the Kinai region.

Odani Castle was a mountain fortress constructed on Odaniyama (elevation 495 meters) in what is now the Kohoku district of Nagahama City, Shiga Prefecture, and it was known as one of the most impregnable strongholds of the Sengoku period through its skillful use of natural fortifications. The Azai clan had ruled over this castle for three generations as the dominant power of northern Ōmi.

The Azai-Asakura Alliance and Its Conflict with Nobunaga: The Breach Between Brothers-in-Law

The relationship between Azai Nagamasa and Oda Nobunaga was initially friendly. Nagamasa married Nobunaga's sister, Oichi, becoming Nobunaga's brother-in-law. However, in 1570 (Genki 1), when Nobunaga attacked Asakura Yoshikage of Echizen, Azai Nagamasa honored his older alliance with the Asakura and turned against Nobunaga. This led to the Battle of Anegawa (Genki 1, 1570), and thereafter the Azai-Asakura allied forces and Nobunaga's army engaged in fierce conflict for three years.

After three years of campaigning, in August 1573 (Tenshō 1), Nobunaga first defeated Asakura Yoshikage in Echizen (the Battle of Ichijōdani), and then turned to a total assault on Odani Castle. With the destruction of the Asakura clan, Azai Nagamasa became completely isolated.

The Assault on Odani Castle: Hideyoshi's Command and the Castle's Structure

The central figure in the assault on Odani Castle was Hashiba Hideyoshi, who would later become Toyotomi Hideyoshi. Hideyoshi was entrusted by Nobunaga with the conquest of northern Ōmi and directed the siege and assault of Odani Castle. This achievement later became the foundation for Hideyoshi's appointment as daimyo of northern Ōmi and his construction of Nagahama Castle.

Odani Castle was a large mountain fortress with multiple enclosures—the main keep, the secondary keep, the Kyōkoku-maru, the Sangō-maru, and the Ōdake—connected along a ridge. Hideyoshi first captured the northern fortifications of the Ōdake and Sangō-maru, and by cutting off communication between the castle's divisions, he separated the defenders. When the Kyōkoku-maru, held by Nagamasa's father Azai Hisamasa, became isolated, Hisamasa took his own life. Nagamasa continued his resistance in the main keep, but in September 1573 (Tenshō 1), the main keep fell, and Nagamasa took his own life after leaving a death poem. He was twenty-nine years old.

Nobunaga's Treatment of the Skulls and the Matter of Swords: "The Skull Chalice" and Sengoku Brutality

After the fall of Odani Castle, Nobunaga had the skulls of Azai Nagamasa, his father Hisamasa, and Asakura Yoshikage lacquered and decorated with gold leaf, and displayed them at a New Year's banquet before the assembled daimyo (this became known as the "Skull Chalice"). This act was later remembered as a striking display of Nobunaga's ruthless assertion of power, and it exemplified the Sengoku-period custom of displaying the heads and remains of defeated enemies to demonstrate one's absolute superiority.

Few detailed records survive regarding the swords used by Azai Nagamasa, but it is reasonable to assume that as a warfield general of northern Ōmi, he carried famous blades from the Bizen and Sōshū schools. Furthermore, after the fall of Odani Castle, Nobunaga confiscated the armor and swords within the castle. It was not uncommon in Sengoku warfare for the weapons caches accumulated at fallen castles to become the spoils of the victor; it is likely that Nobunaga's sword collection included captured weapons obtained from the fall of Odani Castle and other captured strongholds.

Of particular note is the fact that among the commanders of Nobunaga's forces was one who became famous as an owner of the "Heshikiri Hasebe," a celebrated sword. The Heshikiri Hasebe is renowned as one of Nobunaga's famous blades and was later possessed by Kuroda Nagamasa (son of Kuroda Kanbei). Nobunaga rewarded his generals' service in the conquest of Odani Castle not only with land grants but also with swords; the bestowal of celebrated blades thus served as a political instrument to confirm vassal relationships and demonstrate the hierarchy of his warrior contingent.

Akechi Mitsuhide's Participation and the Foreshadowing of the Honnōji Incident

Akechi Mitsuhide also participated in the Battle of Odani Castle. Mitsuhide served under Nobunaga's command as the assigned official for Ōmi and played an important role in the conquest of the Azai and Asakura. However, according to one account, while Nobunaga protected his sister Oichi (the wife of Azai Nagamasa) and placed her under Hideyoshi's protection, Nobunaga's harsh treatment of the Azai clan is said to have created complicated emotions among his vassal band.

As for the motivation behind Akechi Mitsuhide's rebellion in the Honnōji Incident of 1582 (Tenshō 10), various theories have been proposed, but the possibility cannot be denied that Mitsuhide's resentment toward Nobunaga's severe and cruel punishments since the time of the Battle of Odani Castle may have had some psychological impact on him.

The Historical Significance of Odani Castle's Fall: Ōmi Control and Hideyoshi's Rise

The historical significance of the Battle of Odani Castle can be summarized in three points. First, the simultaneous destruction of the Azai and Asakura—the major powers that had encircled Nobunaga—brought Nobunaga's unification of Japan within practical reach. Second, Hideyoshi's performance as the administrator of northern Ōmi was evaluated and later became the "stepping stone" to his position as lord of Nagahama Castle. Third, with northern Ōmi becoming Nobunaga's direct domain, control of Ōmi—a renowned center of sword production—passed into Nobunaga's hands.

Ōmi has since ancient times been an important center of Japanese sword production, and Ōmi swordsmiths had supplied blades to influential warriors throughout the land. The destruction of the Azai clan and the establishment of Nobunaga's rule over Ōmi meant that the patron of this region's swordsmith community changed, leading to a reorganization of sword production under the Oda regime.