Yokoyama-jo Castle (in Omi Province) (横山城 (近江国))

Yokoyama-jo Castle was located in Sakata County, Omi Province (the present-day Horibe and Ishida-cho, Nagahama City, Shiga Prefecture). It was a castle situated on a mountain. It is known as the base of heavy fighting between Nobunaga ODA and Nagamasa AZAI from 1570 to 1573 and the place where Hideyoshi KINOSHITA (the future Hideyoshi TOYOTOMI) defended as a guard when he was the commander of Nobunaga's corps.

Yokoyama-jo Castle was constructed in 1561 on a ridge of the mountain chain on the south side of the Ane-gawa River running between Azai County and Sakata County by Nagamasa AZAI as a base of defense against the Rokkaku clan. Ihiro Azai, from the clan, was appointed as the lord of the castle.

Subsequently, the Azai clan expanded its power from Sakata County to Inukami County, but in 1570 it started a war with Nobunaga ODA, by which the importance of Yokoyama-jo Castle emerged again. Because Yokoyama-jo Castle was located in Sekigahara of Mino Province (the present-day Sekigahara-cho, in Gifu Prefecture) and near the Hokuriku-wakiokan road running through the west side of the base of the Azai clan, Odani-jo Castle (in Kohoku-cho, Shiga Prefecture), and located only six or seven kilometers from Odani-jo Castle, Nobunaga ODA attempted to capture Yokoyama-jo Castle as an important front-line base. On June 28 (old calendar) of the same year, soon after Nobunaga defeated the allied forces of Azai and Asakura at the Battle of Anegawa, he launched an attack on Yokoyama-jo Castle and forced the lord of the castle's Mitamura clan to surrender.

Nobunaga appointed Hideyoshi KINOSHITA as the guard of the castle. Hideyoshi was based in the castle and captured the AZAI clan.

After the AZAI clan was destroyed in October 1573, Hideyoshi, who was given control of Azai County and Sakata County, built Nagahama-jo Castle in Omi Province as his base. It is assumed that Yokoyama-jo Castle fell into ruin around that time.