With that he blew out his candle, put on a great-coat, and set forth in the direction of Cavendish Square, that citadel of medicine, where his friend, the great Dr. Lanyon, had his house and received his crowding patients.
There are no more uses of "citadel" in the book.
Show samples from other sources
If the citadel falls, all is lost.
The New York Stock Exchange is a citadel of capitalism.