The citadel at Besançon towered above the river.贝桑松的要塞高高矗立在河边。

The business is no longer regarded as a citadel of commerce.该行业不再被视为贸易的堡垒。

This modest, not-so-pretty backwater became a citadel of culture.这一朴实无华的落后地区成了文化的堡垒。