网页2024年9月16日 · 城 (shiro, gusuku, ki, shiki, jō): a castle. Kanji in this term. 城. しろ. Grade: 4. kun'yomi. Derivation unknown. The shiro reading for this character appears in 794 CE when the 山背 (Yamashiro) region was renamed 山城, [1] by Emperor Kanmu, thus applying the shiro reading to the 城 kanji for the first time.