The Avesnes fortifications were built in about 1050 around the tower of Wédric le Barbu (Wedric the Bearded). The fortress, on the border between France and the Holy Roman Empire, remained a stronghold until 1873. The earliest fortifications date back to the 11th century and partly encompassed the upper town. In the 13th century, the walls were expanded to unite the lower town with the upper town. After Avesnes was destroyed by Louis XI around 1530, this enclosure was reconstructed as a bastioned system of fortifications. The underground rooms and the Mons door, testimonies of the reinforcements added in the 17th century, were later modified by Vauban when the fortress joined the fortification network of the "Pré-carré" defense lines.