Usayama-jo Castle (宇佐山城)
Usayama-jo Castle was a yamajiro (a castle built atop a mountain to take advantage of the mountain's topography) constructed in the Medieval Period, and its ruins can be found near Nishikoori, Otsu City, Shiga Prefecture. It was located in a conspicuous location along the route to Kyoto on the western coast of Lake Biwa.
Usayama-jo Castle was located at the top of the 336 meter high Mt. Usayama, commanding a full view of Lake Biwa.
Usayama-jo Castle was built by Yoshinari MORI in Shiga County, Omi Province in 1570 by order of Nobunaga ODA, who intended to take control of Lake Biwa and Hokkoku-kaido Road, bracing for the advance of the Asakura clan to the south.
While Oda's main force was assigned to the Battle of Noda-jo Castle and Fukushima-jo Castle which erupted in the Settsu Province in the same year, the Asai and Asakura allied forces started to advance towards Oda, aiming to attack his forces from behind. Yoshinari MORI, the lord of Usayama-jo Castle, attempted to intercept the advance of the allied forces by preemptively conquering Sakamoto (Otsu City), a strategic point of transportation, to help blockade roads along with Nobuharu ODA, the lord of Nobu-jo Castle, and Shigetsuna AOCHI. On October 25, they fended off the allied forces towards the beginning of the war. However, the allied forces were joined by armed priests of Enryaku-ji Temple at the request of Kennyo HONGANJI, and on October 29, the enlarged allied forces invaded the Yoshinari's territory. Although Yoshinari's forces fought bravely by pushing back Kageakira ASAKURA who led the allied forces, they were attacked on the flank by 2,000 soldiers from the Genba and Tsushima ASAI armies. After the main army of Nagamasa ASAI joined the armies of ASAKURA Nakatsukasa, Yoshiie YAMAZAKI, and Saburo AHAKA, Yoshinari's forces finally broke down, leading to the deaths of Yoshinari MORI, Nobuharu ODA, and Shigetsuna AOCHI.
Nobunaga in Settsu, who had heard the news on the 31st and became aware of the situation in Omi, decided to prioritize the battle against the Asai and Asakura allied forces.
On the November 1, he withdrew his main force from 'the Battle of Noda-jo Castle and Fukushima-jo Castle.'
Meanwhile, Usayama-jo Castle had been fiercely attacked by the allied forces that had previously defeated Yoshinari MORI's army in Sakamoto. However, Motomasa KAGAMI, Yoshinari's subordinate, and others strongly fought back along with the castle garrison, and tenaciously held out until Nobunaga arrived in Otsu City to help them on the November 2.