Mont Noir, Border mountain between Saint-Jans-Cappel, Boeschepe and Westouter, France and Belgium

Mont Noir is a 152 m hill shared by Saint-Jans-Cappel and Boeschepe in France and Westouter in Belgium, with the summit entirely on French soil. Its name comes from the black pines in the wood covering the slope. The hill is a Tertiary sand butte capped by iron-rich sandstone; a squat concrete blockhouse with dry grass on top and the graffiti "FMR" stands at its edge.

Between the world wars, Mont Noir was part of a defensive line of blockhouses running from Bray-Dunes to Bailleul, with eight casemates and five blockhouses in the Fortified Sector of Flanders, a component of the Maginot Line. The hill also lay on the Franco-Belgian border, where a customs post operated; tax differences between the two countries drew shops, restaurants and a casino. On the French slope lies Mont Noir Military Cemetery, a First World War burial ground.

The name comes from the De Zwarte family, who owned the hill in the 13th and 14th centuries, though a folk etymology links it to the black pines. Since the 1930s a villa has stood on the site of the lodge of Marguerite Yourcenar's grandmother Noémi Dufresne; the writer described childhood summers here in Archives du Nord. The eight-hectare Parc départemental Marguerite-Yourcenar now holds a writers' residence, and open-air shows are staged there on Sunday afternoons in summer.

The summit lies entirely in France, in Saint-Jans-Cappel, while the slopes fall into Boeschepe and the Belgian Westouter. Climbs start from the French side at Mont Noir, from Vidaigneberg, or via Langendreef and Gemenestraat from Westouter. The last 30 metres of the road to the top are cobbled, and the foot of the hill can flood after heavy rain.

The summit lies entirely in France, yet the slope is shared by three municipalities: Saint-Jans-Cappel and Boeschepe in France and Westouter in Belgium. The Dutch name Zwarteberg comes not from colour but from the De Zwarte family, who owned the hill in the 13th and 14th centuries.