In the past, a citadel was a strong building in or near a city, where people could shelter for safety.
例句
The citadel at Besan?on towered above the river.貝桑松的城堡高高地聳立在河邊。
N-COUNT
（某種生活方式的）庇護所
If you describe a system or organization as a citadel of a particular way of life, usually one you disapprove of, you mean that it is powerful and effective in defending that way of life.
例句
The business is no longer regarded as a citadel of commerce.該行業不再被視為貿易的堡壘。
英漢詞典釋義
n.
城堡,堡壘
The citadel was solid.城堡是堅固的。
英英詞典釋義
Noun
1. a stronghold into which people could go for shelter during a battle