Circumvallation, LINES OF

Circumvallation, LINES OF, form a chain of works surrounding an army engaged in besieging a fortress, but facing outwards towards the country so as to guard against all attempts at relief by a field army. Redoubts, either isolated or connected by a line of parapet, were much used for this purpose in the sieges of the ancient and middle ages; but the greater mobility of modern armies makes it preferable to meet such attempts in the open field, many miles from the position occupied by the investing force. At Sebastopol, owing to the smallness of the besieging force compared with that of the besieged, an outer circuit of redoubts and lines was necessary to keep off the Russian field army, which at Inkermann very nearly succeeded in penetrating this external defence. See CONTRAVALLATION, SIEGE.