1911 Encyclopædia Britannica/Circumvallation, Lines of

CIRCUMVALLATION, LINES OF (from Lat. circum, round, and vallum, a rampart), in fortification, a continuous circle of entrenchments surrounding a besieged place. “Lines of Contravallation” were similar works by which the besieger protected himself against the attack of a relieving army from any quarter. These continuous lines of circumvallation and contravallation were used only in the days of small armies and small fortresses, and both terms are now obsolete.