Bergues was fortified in medieval times, being strengthened significantly in the 14th century by the construction of an extensive wall and many towers. To these defences the Spanish added two crude bastions and built some demi-lunes in front of the gates.
During the 17th century the town changed hands between France and Spain several times before permanently becoming French in 1668. In 1676 Vauban was tasked with strengthening the defences.
Bergues developed around two centres; the Abbey of Saint-Winoc in the east and the lower town in the west, and as a consequence of this the town is a strange figure-of-eight shape. This made it difficult to fortify according to standard fortification principles.
Vauban protected the heights of Saint Winoc (the eastern part of the town) with a crown and two redoubts. He improved the covered way as well as constructing more demi-lunes in the lower town.
The defence of the lower town relied mostly on the ability to inundate the surrounding low-lying ground. Finally, Vauban planned a front of 3 bastions to be built to the north of the lower town, but this work was not carried out until 1744, after he had died.