Yamanaka Castle

Yamanaka Castle is a historic ruin located in Mishima, Shizuoka Prefecture, Japan, originally constructed between 1469 and 1487 by Hōjō Ujiyasu of the Later Hōjō clan. Designed as a yamajiro-style mountain castle, it was strategically positioned on the western slope of the Hakone Pass to overlook the Tōkaidō highway, the vital artery connecting Kyoto with the Kantō region. The fortress featured a long, narrow layout composed of connected enclosures protected by deep wet and dry moats. These moats were uniquely divided into small, checkerboard-like compartments intended to complicate and slow down enemy movements, representing a distinct architectural approach to defense during the Sengoku period.

The castle holds significant historical importance as a frontline defense against rival powers such as the Takeda, Oda, and Tokugawa clans following the collapse of the Imagawa alliance. Its most notable event occurred in March 1590 during the Siege of Odawara, when Toyotomi Hideyoshi ordered its capture to secure his supply lines. Although defended by only 4,000 troops under Hōjō Ujikatsu against an overwhelming force of 50,000, the castle inflicted heavy losses on the attackers before falling in just half a day. Unlike many other fortifications, Yamanaka Castle was never rebuilt during the subsequent Edo period and was left to revert to forest.

Today, the site exists as ruins featuring fragmentary portions of its original earthworks and moats. Despite its destruction over four centuries ago, the location has been preserved and designated as a National Historic Site of Japan since 1988. It remains open to the public, allowing visitors to explore the unique defensive structures that once guarded one of Japan's most critical travel routes.