was a Muromachi period yamashiro-style Japanese castle located in what is now part of the city of Tonami, Toyama Prefecture in the Hokuriku region of Honshu, Japan. The ruins have been protected by the central government as a National Historic Site since 2009. It was also known as Background Masuyama Castle is located on a 120-meter hill in the mountainous area which separates the Tonami Plain from the Toyama Plain in Etchū Province. This location is on the border of the three counties of Tonami, Imizu, and Nei, and the castle could command the major transportation route within the province. Although the Hokuriku kaidō, a highway which connected Kyoto with the Hokuriku region, passed Kurikara Pass at the border of Kaga Province and followed the Shokawa River to Toyama Bay avoided this area by taking a coastal route, the more direct route passed through this hilly area and Masuyama Castle was located to guard this strategic area. Masuyama Castle is a regarded as one of three major mountain castles of Etchū Province along with Moriyama Castle near the Noto Peninsula and Matsukura Castle in Uozu area. History The foundation of Masuyama Castle was founded during the Nanboku-cho period by Momonoi Tadatsuna (d.1376), the shugo of Etchū Province. The name Wada Castle came from the nearby Wada River. Momonoi later revolted against the Ashikaga shogunate, and the castle was seized by a shogunal army and awarded to the Ninomiya clan, but the castle fell into ruins shortly after the conclusion of the campaign. Around a hundred years later, the castle was rebuilt as a stronghold of the Jinbō clan, retainers of the Hatakeyama clan, who had been awarded with the position of shugo of Etchū Province. The Hatakeyama preferred to rule in absentia from Kyoto, and the province was sub-divided between the Jinbō, Shiina and Yusa clans to administer on their behalf. By the end of 15th century, Hatakeyama clan was significantly weaker and unable to exert their authority over Etchū. Jinbo Yoshimune (d. 1531) attempted to ally with the Ikkō-ikki movement and to become independent, but was crushed by the Hatakeyama and by the forces of the Uesugi clan from neighbouring Echigo Province. However, his son Jinbō Nagatomo (d.1572) took advantage of internal conflicts within the Hatakeyama and the Uesugi and surpassed the rival Shiina clan, uniting the province and established Toyama Castle, with Masuyama Castle remaining an important secondary