Fort du Bois d'Oye, Fortress in Bermont, France

The Fort du Bois-d'Oye is a pentagonal limestone fortress with walls around a large open court, built into a grassy mound at 420 meters. Its grey masonry facade has a central arched tunnel with a red-painted vaulted interior, flanked by deep arched recesses and topped by a parapet with narrow openings. A well and cistern supplied water.

The fort was built between 1883 and 1886 as part of a defensive ring protecting Belfort. It followed the military building principles of the Séré de Rivières system that shaped French fortresses of that era.

The fort reflects how French military planners of the late 1800s thought about defense through its position overlooking key transportation routes. This location allowed soldiers to monitor both railway lines in the region.

The fort is not open to the public; visits are led by members of the Bermontfort association, and the site opens for the European Heritage Days. The Bois d'Oye is one of eight Séré de Rivières forts in the Belfort belt, linked by a 79 km long-distance walking route.

The fort's garrison numbered 624 soldiers, 32 non-commissioned officers and 17 officers, and its initial armament included 17 155mm long guns, 5 120mm long guns and 2 220mm mortars. In 1890 a 247-place personnel shelter was built north of the fort, on the commune of Dorans, later used as a command post for the southern sector of the Montbéliard defensive sector under the Maginot Line.