The Château de Brest is a castle in Brest, Finistère, France. The oldest monument in the town, it is located at the mouth of the river Penfeld at the heart of the roadstead of Brest, one of the largest roadsteads in the world. From the Roman castellum to Vauban's citadel, the site has over 1700 years of history, holding right up to the present day its original role as a military fortress and a strategic location of the highest importance. It is thus the oldest castle in the world still in use, and was classified as a monument historique on 21 March 1923 [1].

Its structure has continually been rebuilt over the centuries to defend against all attacks by land and sea. Its heterogeneous architecture is thus the result of the defences' continual adaptation to new developments in siege warfare and armament.