Niyama Castle

Connection to Swords

The connection between Niyama Castle and Japanese swords can be understood from two perspectives: the iron resources and blacksmithing culture of the Izu and Sagami regions where the castle stood, and the sword policies of the Later Hōjō daimyo clan. Izu Peninsula has been known since ancient times as a source of iron sand (Izu-tetsu). Rivers flowing from the Izu mountains were rich in iron sand, and iron production and blacksmithing using it as raw material had continued since the medieval period. In particular, the area of Tagata County north of Niyama was known as a region where blacksmiths congregated, and records show the Later Hōjō clan organized these local smiths to support the production of military supplies including swords, armor, and firearm components. The Later Hōjō clan, which ruled the Kantō, Izu, and Sagami regions for five generations over 100 years, required vast quantities of swords and armor to maintain their large military forces. The Hōjō clan placed subordinate swordmakers and blacksmiths under the jurisdiction of a "Sword-Smith Commissioner" and constructed an organized system of weapons production. Sagami (Kanagawa Prefecture) was a center of swordmaking that produced some of the highest peaks of Japanese swordsmithing, known as the Sōshū tradition, and birthed legendary smiths such as Masamune, Yukimitsu, and Hiromitsu. The Later Hōjō base at Odawara lay within the Sōshū tradition's sphere of influence, and Niyama Castle functioned as a forward base to the south. The Niyama Reverberatory Furnace of the late Edo period (UNESCO World Heritage site) is intriguing as a modern evolution of the relationship between Western-style blacksmithing and iron production technology and Japanese sword craft. The reverberatory furnace is a facility that cast cannons using molten iron, and in terms of 'the technique of working iron,' it shares the same cultural lineage as katana-forging technology. From ancient iron-sand iron production to modern iron manufacturing in the late Edo period, Niyama embodies the continuous development of 'Japan's iron technology' and occupies a unique place in the context of sword history.