The Citadelle of Quebec, also known as La Citadelle, is an active military installation and the secondary official residence of both the Canadian monarch and the governor general of Canada. It is located atop Cap Diamant, adjoining the Plains of Abraham in Quebec City, Quebec. The citadel contains the oldest military building in Canada, and forms part of the fortifications of Quebec City, which is one of only two cities in North America still surrounded by fortifications, the other being Campeche, Mexico.
The strategic importance of Cap Diamant was recognized by the French as early as 1608. Several defensive fortifications were built on the site first by the French, and then by the British after their conquest of New France. The modern citadel was built from 1820 to 1850, in effort to secure Quebec City against a potential American attack. The British used the citadel until 1871, when they formally handed the property over to the Canadian government. Following the handover, the citadel was used as a military installation by the Canadian Armed Forces, and as a royal and viceregal residence.