The site of Oshio castle is located on the Daikouji Mountain just behind the Kuchidano village. It is a hill, 134.7m in height, but it was the place of strategic importance where it is possible to see every points of Minamigawa valley. There is the Daikouji on foot of the mountain, and there are the place named Yakata or Yakatanokuchi. According to Kuchinatasonshi, the castle was built by Yoshinobu Oshio, who was the server of Takeda family, in Kanei 6(1465) and the temple was built in Bunmei 1(1469). But according to Gunkenshi, it doesn't mention about building the castle, but it tells that Yoshitsugu Oshio built the Daikouji in Meiou 2(1493) and passed away in Eisho1(1504).
The front approach comes from the Daikouji and there is a plateau for castle on the top of mountain, 100m wide and 50m deep. There is a hollow in south side of the plateau and a bridge divides the hollow into 5 areas, it is often seen in Kanto area, but it is rare in Kansai area except the one in Nara.
Oshio family has been ranked "Nagatonokami" for ages. According to the Kuchinatasonshi, it mentions 4 generations, Yoshinobu, Yoshitsugu, Yoshitada and Sukehide. But according to Gunkenshi, it mentions 3 generations, Yoshitsugu, Shinzaemonnosyo Yoshitada, Hachirouzaemon. It is considered that Yoshinobu and Yoshitsugu is the same person, as Yoshitsugu's Hougou is Daikouji. The last lord of the castle fought against the Hisakata Nanbu, the lord of Yunooka castle in Eiroku 5(1562), but he was defeated and asked Awaya family to protect him.
Explanation 
Kuchidano ku
