CIRCUMVALLATION

Etymology

From circumvallate.

Noun

circumvallation (plural circumvallations)

A rampart or other defensive entrenchment that entirely encircles the position being defended.

Source: Wiktionary

Cir`cum*val*la"tion, n. (Mil.) (a) The act of surrounding with a wall or rampart. (b) 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 Unabridged Dictionary 1913 Edition