Kanayama Castle (Nitta Kanayama Castle)

Kanayama Castle (Kanayama-jō) is a Sengoku-period mountain castle built on the summit of Mount Kanayama (239 m above sea level) in Ōta City, Gunma Prefecture. It was constructed in Bunmei 1 (1469) by Iwamatsu Iezumi, a powerful local lord of Kōzuke Province. It stood on the site of the stronghold of Nitta Shō (Nitta no shō), the castle seat of the Nitta family (descendants of Minamoto no Yoshiie and members of the Nitta Yoshisada line). Built on a strategic site with a commanding view of the Kantō Plain, it earned its place in Sengoku history as 'a famed castle of the Kantō' and 'the impregnable Kanayama Castle.' It is also known as 'Ōta Kanayama Castle.'

The castle used a renkaku-shiki nawabari (layout of connected enclosures) that spread along the entire ridge from the summit of Mount Kanayama, with the Honmaru, Ninomaru, Sannomaru, Baba kuruwa, and Monomidai placed along the ridgeline. Notably, stone walls and stone paving are used extensively. The castle is valued as an important site that, through excavation, overturned the long-held view that Sengoku-period mountain castles in the Kantō had no full-fledged stone walls. Nozura-zumi stone walls coexist with earthen features such as horikiri (dry ditches) and dobashi (earthen bridges), making it a fine example of how the defensive system of mountain castles changed over time.

Control of the castle passed from the Iwamatsu family, who built it. Around Kyōroku 1 (1528), retainers Yokose Yasushige and his son Narishige killed their lord Iwamatsu Masazumi and seized power (the Kyōroku Disturbance). Around Eiroku 8 (1565), Narishige changed his surname to Yura, and the castle became a castle of the Yura family. During the Yura period, Kanayama Castle functioned as a political base in Kōzuke Province while the Yura repeatedly fought, allied with, and broke from the Later Hōjō. In Tenshō 2 (1574), it also fought against the forces of Uesugi Kenshin. In Tenshō 12 (1584), the brothers Yura Kunishige and Nagao Akinaga were called to account by the Hōjō. Their mother, Myōin-ni, along with clan members and retainers, held out in Kanayama Castle, but it is thought they surrendered the castle and submitted to the Hōjō by spring of that same year.

Kanayama Castle had been handed over to the Hōjō in Tenshō 13 (1585). During Toyotomi Hideyoshi's attack on Odawara in Tenshō 18 (1590), it was seized as a castle in Hōjō territory and was abandoned thereafter. Meanwhile, Yura Kunishige was detained at Odawara Castle, but because his mother Myōin-ni and others sided with Hideyoshi, the Yura family survived the war and was granted domains in Ushiku, Hitachi. After its abandonment, many remains such as stone walls were left in place. Today, as 'Kanayama Castle Ruins,' it is a nationally designated historic site and is counted among the Nihon Hyakumeijō (100 Famous Castles of Japan). It has been developed as a historic park maintained by Ōta City. Another attraction is the magnificent view from the castle ruins, which overlooks the Kantō Plain, Mount Asama, Mount Akagi, Mount Haruna, and others.