Bouchain is a small town situated midway between Valenciennes and Cambrai (also fortified places) and was strategically important due to its situation at the confluence of the rivers Escaut and Sensée. The town is divided into an upper town (which later became the citadel) on the high ground west of the river and a lower town in the marshy ground on the east bank. The upper town had a castle from the 7th century and town walls from the 12th century, when the town passed to the Counts of Hainaut.
The upper town was fortified by Charles V in 1532. He had a strong square bastionned citadel with demi-lunes and a ditch built to protect it.
In 1676, Bouchain fell to the armies of Louis XIV and the fortifications were strengthened by Vauban. The lower town was protected by earthwork defences, which stretched eastwards from the citadel, ending with a hornwork and demi-lune.