(in the past) a castle on high ground in or near a city where people could go when the city was being attacked （旧时的）城堡，要塞，堡垒 After the Mongol invasion of 1241, a citadel was built on the hills opposite the city. 蒙古在1241年入侵后，在这座城市对面的山上建造了一座城堡。 - (figurative)
citadels of private economic power 私人经济力量的堡垒
Word Originmid 16th cent.: from French citadelle, or from Italian cittadella, based on Latin civitas ‘city’, from civis ‘citizen’.