"城郭" (jōkaku) refers to the fortified structures and walls that surround a castle in Japan. These structures were designed for defense and protection, often featuring moats, gates, and watchtowers. They played a crucial role in the military strategy of feudal Japan, helping to secure the territory of the ruling samurai. The design of 城郭 varied by region and period, reflecting the architectural styles and materials available at the time. Many famous castles, such as 姫路城 (Himeji Castle) and 大阪城 (Osaka Castle), showcase the beauty and complexity of these fortifications, which are now important cultural heritage sites.