The Maubeuge fortified sector, part of the old Great War era fortress line along the Belgian border, had been re-built along the Sambre River as a kind of secondary extension of the Maginot Line. Following the Allied Dyle plan's failure and subsequent German moves southward to cut off the French armies' retreat, some utterly exhausted French troops filed into the Maubeuge fortifications to join those garrisons that had not been drawn off into the fighting elsewhere. Hopefully, they could delay the German advance long enough to help the French form a new line of resistance.

A cluster of casemates at Marpent defended the south bank of the Sambre, while on the north bank a mixed collection of French units under Lt. Col. Eugene Marioge of the 6th Tirailleurs Marocains fought desperately to defend the few bridges which had not yet been destroyed. The Germans attacked the southern casemates on the morning of the 18th and took them one by one that afternoon despite powerful defensive fire from the nearby fort at Boussois. Meanwhile, Germans coming from the city ofMaubeuge hit the French from another direction. On the Assevent bridge, scattered infantry and several tanks resisted repeated German attempts to cross the river and held the bridge until nightfall. Groupement Marioge held out for several days, but their fate was sealed from the outset. The fort at Boussois, the last of the Mauberge Line to fall, capitulated under massive bombardments and engineer attacks on 21 May.