Noun
The act of surrounding with a wall or rampart.
A line of field works made around a besieged place and the besieging army, to protect the camp of the besiegers against the attack of an enemy from without.
Source: Webster's dictionaryA line of circumvallation would also be constructed, facing in towards the besieged area, to protect against sorties by the defenders and to prevent the besieged from escaping. Source: Internet
As a siege progressed, the surrounding army would build earthworks (a line of circumvallation ) to completely encircle their target, preventing food, water, and other supplies from reaching the besieged city. Source: Internet
The circumvallation and Battle of Alesia in 52 BC; the women and children of the encircled city were evicted to conserve food, where they starved to death between the opposing walls of the defenders and besiegers. Source: Internet
The Roman legion surrounded Masada, built a circumvallation wall and then a siege ramp against the western face of the plateau. Source: Internet