Fort de la Fraternité, Military fort in Roscanvel, France.

Fort de la Fraternité is a ruined stone fortification on the îlot du Diable, built around a 1695 gun battery. Its rough grey and brown masonry forms a crenellated upper wall and a rounded bastion pierced by a large arched tunnel entrance, with a smaller arch higher on its left. A low parapet borders the grassy slope, and a gunpowder magazine with large rectangular roof slabs still stands.

A gun battery from 1695 was replaced by this fort built in 1791, which then became part of the defense network protecting the Brest area. Military use stopped in 1870, and the site was left behind.

The fort's name, "Fort of Brotherhood", contrasts with its role in defending the goulet de Brest. The site also includes a lime kiln built in 1800 against the southern slope, which produced lime for local and military construction until 1875. Its rough exterior mixes limestone with white calcite veins and yellowish microgranite blocks.

The fort stands on the îlot du Diable opposite the Roscanvel shore, so it is reached by boat across the water of the goulet de Brest; check sea and weather conditions before setting out. The ruins are unstable, and the lime kiln on the southern slope is dangerous because of falling stones and possible collapse.

The site once held a limestone seam that was mined until 1875, and a lime kiln from 1800 still stands visible today. This early industrial use makes the place more than just a military structure.