1. fortified areas or strongholds, typically on high ground protecting or dominating a city
2. places or situations of refuge; strongholds of particular activities, attitudes, or beliefs
Usage: figurative

Examples

• The ancient citadels overlooked the valley below.
• Medieval citadels were built to withstand long sieges.
• The university became one of the last citadels of classical education.
• These institutions remain citadels of tradition and conservative values.
• The hilltop citadels provided excellent defensive positions.
• Several citadels still stand as monuments to military architecture.