Citadelle de Montreuil-sur-Mer, 13th-century military citadel in Montreuil-sur-Mer, France
The citadelle de Montreuil-sur-Mer is a 13th-century pentagon-shaped fortress with five bastions and ancient royal gates reinforced by two towers. Its walls display military architecture that evolved across multiple periods, creating a layered structure of defense and stone.
After troops of Charles V ransacked the city in 1537, King Charles IX ordered construction of one of France's first bastioned citadels on the site of a former royal castle. The building was later reinforced and adapted to meet changing military needs over the centuries.
The fortress served as a military command center during World War I and now displays exhibitions about that period. Visitors can see how the building functioned during wartime and understand its strategic importance then.
The site is easy to explore on foot with clear paths along the walls and through the bastions. Wear comfortable shoes, as some areas involve stairs and uneven ground.
The fortress is a breeding site for Greater Horseshoe Bats, a rare species that roosts and nests within its chambers. This ecological role led to its designation as a Natura 2000 conservation area in northern France.
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