circumvallation

Circumvallation, from Latin circumvallatio meaning "a surrounding rampart," is a line of fortifications erected by an attacking army to encircle a besieged fortress or town. The purpose is to prevent relief forces from breaking the siege, to cut off supplies, and to provide secure positions for siege artillery and tracing lines of attack. The construction typically proceeds from the besieging army’s main camp and forms a continuous wall around the target, often including trenches, ramparts, glacis, covered ways, redoubts, and artillery batteries; outworks such as ravelins or tenailles may be added to improve flank protection. In many cases, a separate contravallation line—built outward from the circumvallation to guard against relief troops approaching from outside—was also constructed.

Historical development: The concept was widely used in early modern warfare, particularly in the 16th to 18th centuries. Notable examples include the Antwerp siege of 1584–1585, where the attackers established both circumvallation and contravallation to isolate the city. The method was expanded and refined by European engineers such as Vauban in France and Coehoorn in the Netherlands, whose siege works emphasized powerful artillery positions and reinforced defensive circuits. With the evolution of warfare and artillery, the use of formal circumvallation lines faded by the 19th century, though the term remains a standard description in military history.

Legacy: The remains of circumvallation lines are important sources for understanding siege operations and military engineering in the early modern period.