Fort du Haut-Buc, Military fortification in Buc, France.

Fort du Haut-Buc is a large trapezoidal fort on the Saclay plateau, built of rough light-brown stone, with a cavalier for 820 men and 56 guns. Its counterscarp gate and escarpment gate keep their original fittings, and two stables with their mangers remain in the counterscarp. A covered passage with a segmental-arch vault leads to the officers' pavilion, which has four casemates for indirect fire.

Built from 1874 and completed in 1879, the Fort du Haut-Buc was one of 18 forts, 5 redoubts and 34 batteries raised between 1874 and 1881 under the Séré de Rivières system, the programme of fortifications drawn up to defend Paris after the Prussian occupation of 1870. It formed a pair with the fort de Villeras at Saclay, supported by five outlying works. Its trapezoidal plan with a cavalier was sized for 820 men and 56 guns, and its fire crossed that of Villeras. A 1911 project for a 75 mm turret and machine-gun turret was never carried out; the fort was damaged in the fighting of August 1944.

The fort's name comes from the Haut-Buc plateau in Buc, and its two entrance gates keep their original fittings apart from the retractable rolling bridge, of which no trace remains. In the counterscarp, two stables with their stone troughs are still visible. The site is now closed to the public.

The site is not open to public access as it serves as a training ground for law enforcement and maintains restricted military status. External views are possible, but the interior remains closed.

The fort's two counterscarp stables still keep their original stone troughs, visible in the ditch. Behind each of the small fronts, a large powder magazine sits under brick vaults, entered through a sizeable airlock and still fitted with its original door and window frames.