Asonuma Clan, one of the local powerful clans of Tono district (present day Iwate Prefecture) removed and reconstructed a castle in this place during the Tensho era (1573-91). In 1627, Naoyoshi Nanbu of Nejo Castle in Hachinohe was enfeoffed this region and he changed the name of the castle to Nabekura Castle. This mountain castle stood at the top of Mt. Nabekura at 340 m altitude, which is an independent hill located at the foot of Mt. Monomiyama in the south of Tono Basin. The castle remains existing at the present were of those constructed in the early modern times. Honmaru (the main compound) originally had a thatched roof, but after the fire broke out during the Keian era (1648-52), the roof was thatched with Japanese spindle tree. Honmaru used to be walled with wooden fences. There was a housing area of warriors at the west, north, and east foot of the mountain, outside of which spread townsmen’s houses. There were also three Doshin (feudal police) offices at the end of the town; Shimo-gumi office was located at the west end, Naka-gumi at the north, and Kami-gumi at the east. Nabekura Observatory, which looks like a donjon, was constructed at Sannomaru ruins.