1. a castle intended originally for the defence of a city, usually built on a high place
2. a place that seems to represent all the important aspects of an idea, method, or practice
Origin and usage
The word comes from the French ‘citadelle’, or from Italian ‘cittadella’, both of which were based on the Latin word for city, ‘civitas’. Both words are diminutives, meaning literally ‘little city’.
A citadel is a fortress, typically on high ground above a city, but sometimes at the heart of the city itself. It is strongly fortified so that the city’s inhabitants can withdraw there and defend themselves in case of attack. Structures identified as citadels have been identified dating as far back as 3000 BCE and a citadel was a feature of many cities in ancient Greece, where it was called ‘acropolis’, which means ‘high city’.
The metaphorical meaning of citadel derives from the idea of it as a stronghold. A citadel of learning, therefore, is a place where learning has top priority while a citadel of democracy is one that places democracy above everything else and will defend it against all-comers.
“It appears to me that almost any man may like the spider spin from his own inwards his own airy citadel.”
castle, fort, fortress