Yamanaka Castle

Yamanaka Castle, located in Mishima City, Shizuoka Prefecture, was a medieval mountain castle originally built in the Yamanaka area of Tagata District in Izu Province. It is now designated as a National Historic Site of Japan. Constructed by the Hōjō clan during the Sengoku period, it served as one of the branch castles of Odawara Castle and was an important stronghold among the “Ten Castles of Hakone.”

The history of Yamanaka Castle dates back to the Eiroku era (1558–1570), when Hōjō Ujiyasu ordered its construction to protect the western approaches to Odawara Castle, the clan’s main base. Strategically located along the Tōkaidō highway, the castle was designed for both military defense and control over transportation routes. During the later years of Hōjō rule, as tensions with Toyotomi Hideyoshi escalated, the castle underwent expansions and fortifications to strengthen its defenses. However, when Hideyoshi launched the Siege of Odawara in 1590, Yamanaka Castle was still incomplete and faced the overwhelming force of Toyotomi’s army.

Toyotomi Hidetsugu led approximately 68,000 troops against the castle, which was defended by only about 3,000 men under Hōjō Ujimasu, Matsuda Yasunaga, and Mamiya Yasutoshi. Despite fierce resistance—particularly by Mamiya Yasutoshi, who fought with 200 men in the San-no-maru and Taisaki Demaru areas, inflicting heavy casualties on the attackers, including the death of commander Ichiyanagi Naomune—the defenders were overwhelmed. The castle fell in less than half a day. Following its capture, Yamanaka Castle was abandoned and became a historical ruin.

Yamanaka Castle is notable today not only for its historical significance but also for its well-preserved defensive structures. Because it was abandoned immediately after the fall of the Hōjō clan and never rebuilt in later periods, it retains the distinctive features of Sengoku-period Hōjō-style castle construction. The most iconic elements are its une-hori (ridged moats) and shōji-bori (lattice-pattern moats), ingenious defensive designs that have been restored and maintained, making the site an important resource for archaeology and architectural history.

Designated as a National Historic Site since 1930, Yamanaka Castle has been maintained as a historical park by Mishima City since 1973, with ongoing academic research. In 2006, it was listed as No. 40 among the “Japan’s Top 100 Castles.” Until recent years, the third Sunday of May was celebrated with the “Yamanaka Castle Festival,” offering castle tours and historical reenactments, though the event is no longer held.