investment (military)

Investment is the military tactic of surrounding an enemy fort (or town) with armed forces to prevent entry or escape.A circumvallation is a line of fortifications, built by the attackers around the besieged fortification facing towards the enemy fort (to protect itself 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 the city.
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