Investment (military)

Investment is the military process of surrounding an enemy fort (or town) with armed forces to prevent entry or escape. It serves both to cut communications with the outside world, and to prevent supplies and reinforcements from being introduced.

A circumvallation is a line of fortifications, built by the attackers around the besieged fortification facing towards an enemy fort (to protect the besiegers from sorties by its defenders and to enhance the blockade). The resulting fortifications are known as 'lines of circumvallation'. Lines of circumvallation generally consist of earthen ramparts and entrenchments that encircle the besieged city. The line of circumvallation can be used as a base for launching assaults against the besieged city or for constructing further earthworks nearer to the city.