Siege of Ishiyama and Imakatata Castles
Date: Second month of Genki 4 (1573)
Location: Ishiyama and Imakatata castles in Ōtsu in Ōmi Province
Synopsis: In the second month of Genki 4 (1573), Ashikaga Yoshiaki raised arms against Oda Nobunaga and fled from the capital of Kyōto to Ōmi Province. He then set about to rally local clans to join in opposition to Nobunaga. Nobunaga responded by dispatching four senior retainers to lead an army to attack Yoshiaki at Ishiyama and Imakatata castles near Lake Biwa. By the end of the month, both castles had fallen to the Oda.
Shōgun: Ashikaga Yoshiaki
Commanders: Yamaoka Kagetomo, Isogai Hisatsugu, Watanabe Shō, Yamamoto Tsushima-no-kami, Iga Group, Kōka Group
Losses: 500 killed and over 1,000 wounded
The Siege of Ishiyama and Imakatata Castles occurred in the second month of Genki 4 (1573) in Ōtsu near the shores of Lake Biwa in Ōmi Province. The conflict was waged between Oda Nobunaga and Ashikaga Yoshiaki, the fifteenth (and last) shōgun of the Muromachi bakufu.
In the second month of Genki 4 (1573), Ashikaga Yoshiaki raised arms at the Nijō Palace in Kyōto against Oda Nobunaga.
By the middle of the same month, Yoshiaki endeavored to rally the kunishū, or provincial landowners, in the Shiga and Takashima districts of Ōmi including in Ishiyama and Imakatata to join forces against Nobunaga. Yamaoka Kagetomo, Isogai Hisatsugu, Watanabe Shō (Kunai-Shōyū), and Yamamoto Tsushima-no-kami responded by dispatching troops to Ishiyama and Imakatata and joined Yoshiaki in his revolt.
A journal entry from 2/6 indicates that there were some intending to betray Iwakura Yamamoto, Watanabe Shō, Isogai Hisatsugu, and Akechi Mitsuhide, suggesting that there were some defectors among those under the command of Mitsuhide.
On 2/24, the Oda army departed from Seta to cross Lake Biwa and attack Ishiyama Castle. Ishiyama Castle was defended by Yamaoka Kagetomo leading the Iga Group and the Kōka Group. On 2/26, the garrison surrendered and vacated the castle which was then destroyed by the Oda army.
On 2/29, the Oda army attacked Imakatata Castle located on the shores of Lake Biwa. From around 8:00 AM, Akechi Mitsuhide utilized naval vessels on Lake Biwa from the east to launch an attack from the water. Mitsuhide also controlled the maritime rights on the lake. Meanwhile, Niwa Nagahide and Hachiya Yoritaka charged from the southeast. Around noon, the Akechi battalion breached the castle defenses and achieved victory.
After subduing Imakatata, Mitsuhide went to Sakamoto Castle and the other three commanders returned to their home base.
In this battle, Yoshiaki’s army lost 500 soldiers and had over 1,000 wounded, attesting to the scale of the conflict. He did not receive any reinforcements from the Azai or Asakura clans. In the Akechi battalion, a total of eighteen soldiers were killed in action.