inner castle; main keep; innermost enclosure
Refers to the central, most fortified area of a Japanese castle, often containing the main keep (天守). Contrasts with 外城 (そとじろ/がいじょう), the outer castle or enclosure.
See also: 外城
The inner castle was the most important defensive stronghold of the castle.
The main keep towers over the inner enclosure of this castle.
Compound of 内 (ない, 'inner') and 城 (じょう, 'castle'). The reading じょう is the on'yomi of 城, commonly used in Sino-Japanese compounds.