Hirabayashi Castle

Hirabayashi Castle (平林城) was a Sengoku period Japanese castle located in the city of Murakami, northern Niigata Prefecture, Japan. The site has been protected by the central government as a National Historic Site since 1978.

Background
Hirabayashi Castle is located on top of Mount Yōgai, a 200-meter hill near the mouth of the Arakawa River, and at the northern edge of Echigo Plain. The area is more than 200 kilometers from the Jōetsu area, which contained the provincial capital, and was isolated from Dewa to the north and east by mountains.

History
During the Sengoku period, northern Echigo was controlled by a number of petty lords known as the “Agakitashu”, who were originally the magistrates sent by absentee landlords to administer shōen manors in the area during the Kamakura period. Over the centuries, the position became hereditary, and these magistrates became virtually independent. The Hirabayashi area was originally controlled by the Hirabayashi clan, the original builders of the castle. However, during the Nanboku-chō period, their territory was seized by the Irobe clan. The Irobe were a cadet branch of the Taira clan from the Chichibu region of what is now Saitama Prefecture and were thus related to the Honjō clan of neighbouring Murakami Castle. At the beginning of 16th century, the Nagao clan, a cadet branch of the Uesugi clan grew in power in southern Echigo. During an internal conflict between different branches of the Nagao, the Irobe supported Nagao Fusayoshi, the shugo of Echigo against Nagao Tamekage, the deputy shugo. Tamekage ordered the Nakajō clan, a powerful neighbour to attack Hirabayashi Castle. The castle eventually fell, and the Irobe were forced to pledge fealty to Nakao Tamekage.

The Irobe revolted when Nakao Tamekage was replaced by his son, Nakao Harukage, but when Uesugi Kagetora (Kenshin) succeeded Harukage, the Irobe became his retainers. Probe Katsunaga (1493-1569) achieved distinction at the fourth Battle of Kawanakajima in 1561. During the 1563 campaign against the Odawara Hōjō, he captured Sano Castle in Kōzuke and was ranked as seventh among Kenshin's generals.

After the death of Kenshin in 1578, the Irobe supported his successor Uesugi Kagekatsu. However, in 1598, Uesugi Kagekatsu was transferred to Aizu by Toyotomi Hideyoshi, and the Irobe also accompanied him. Hirabayashi Castle was abandoned and fell into ruin afterwards.

Design of Hirabayashi Castle
Hirabayashi Castle was typical of Sengoku period mountain forts in that it consisted of several enclosures spread across a long and narrow ridge, utilising the natural terrain as part of its defences. The inner bailey is located at the top of the mountain, and is roughly pentagonal in shape, and was protected by a simple clay wall. The main gate to the inner bailey as a large "masugata" gate.