Yamanaka Castle, established by Hojo Ujiyasu in the 1560s, is located in what is now eastern Mishima, Shizuoka Prefecture. This castle served as the first line of western defense for the main Hojo Castle at Odawara. Carved into the side of a 586-meter-high mountain, Yamanaka Castle was strategically positioned along the Tokaido Highway, offering superb views of nearby Mt. Fuji, the ocean, and the road leading to Odawara.

The castle featured five baileys: the Honmaru, Ni-no-Maru, Kita-no-Maru, Nishi-no-Maru, and the Daisaki-de-Maru. These compounds were fortified with well-defended gates, log palisades, and wooden walls equipped with gun and arrow slits. Intricately designed dry moats and steep slopes further protected the castle. Notably, Yamanaka Castle’s unique Shoji-bori and Une-bori moats, which are waffle-shaped with narrow ridges surrounding square depressions, can still be seen and appreciated today. These dry moats were necessary as sourcing and maintaining water at the top of the mountain was impractical.

In 1587, as Toyotomi Hideyoshi neared the complete unification of Japan, he set his sights on the Hojo clan, who had not yet submitted to his rule. As he raised large armies against them, the Hojo fortified their smaller outlying castles, including Yamanaka, which was commanded by Hojo Ujikatsu and supported by around 4,000 samurai. However, these fortifications were incomplete when Hideyoshi made his move in 1590. The Toyotomi army, numbering around 67,000, vastly outnumbered the Hojo defenders at a ratio of 16 to 1. Despite this, the Hojo troops fought valiantly, inflicting heavy losses on the Toyotomi forces. The battle, which lasted barely half a day, or according to some accounts, as little as two hours, ended in the deaths of most defenders and the destruction of the castle. Hojo Ujikatsu and his top generals fled to assist in the defense of Odawara Castle. This battle marked the first skirmish in the Siege of Odawara, leading to the downfall of the Hojo clan.

Declared a National Historic Site in 1934, Yamanaka Castle had reverted to forest, prompting preservation projects to restore its remains. Although no structures remain, the distinctive Shoji-bori and Une-bori moat systems are still visible and appreciated. These moats, with their narrow ridges, ensured attackers could only cross in single file, making them easy targets for defenders. The ridges likely featured wooden spikes and tied ropes to further hinder attackers. In 2006, Yamanaka Castle was listed among the Top 100 Castles of Japan.


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